It's not that it's going to make it too powerful, it's that this is not what skills DO. And really, making it a skill is akin to making a class based solely around the Tumble skill and having no other real abilities that do anything without said skill. Sure there are classes that use the Tumble skill to great effect, but no class is solely about using that skill to kill things.
Which is what attracted me to the Truenamer class to begin with. And when you think about it, Epic Spellcasting does use Spellcraft to help kill things.
That's what I'm doing with this. The Truespeak check itself isn't needed
to use Utterances, it just improves them beyond the bare minimum effect to the point where they are actually useful. In effect the skill isn't killing them, the SLA is. The skill is just helping to make you more efficient at killing them.
Then you get into some more problems with skill boosting items which does actually mess with the balance a lot (if you take a +30 item (ignoring miscellaneous bonus items like luck, morale, Tedisawesome, etc.) you are pretty much twice as powerful as someone who didn't. Normally, not a problem, but since this makes it practically a requirement to take an item, that's reliance on items right there, or you're overpowered with items). If it was a class based bonus, like class level+1/2 other class levels+some miscellaneous to get the bonus to where you want in class, then you have more control over the bonus amount, can balance it a heck of a lot easier, and the class isn't dependent on an item.
That's something I'm painfully aware of. I'm taking cautious steps to avoid them becoming all-powerful by putting a hard cap on the abilities their utterances can duplicate. The Polymorph utterance I have listed up there? Limited to one of 4 forms based on the skill check's result. Those choices are set in stone and cannot be altered beyond the utterance itself.
Even at the highest possible skill check result, it just makes them into a Warlock. It alters the class the same way optimizing alters any class; by raising it one to two Tiers in power. Having a base Truespeak check of +70 just means you have a long time before you actually have to start rolling to beat the DC due to the Law of Resistance (yes, I kept it). It means you are going to be on par with other spontaneous casters in terms of sheer versatility, but you won't have the game-breaking material they have and will eventually run out of steam yourself (it takes a while though). It's akin to a Sorcerer going into Incanatrix to make his spells awesome, or an Erudite taking Spell To Power. Only less horrifically broken.
I'm trying to make this fix as close as possible to the original idea that WotC put into the book while still making the fix playable and reasonably balanced. This fix assumes the DM is using common sense, such as disallowing Item Familiar and restricting custom magic item creation (because those are easily abused, and broken in their own right). Both of these are optional on the DM's behalf, so if the DM allows it then it isn't the class fix that's the problem.
Yes, I'm stepping into the Oberoni Fallacy. I'm also assuming the people who will use this fix are competent gamers who use rational thinking when optimizing their characters or when allowing specific material. The ones who allow incredibly abuseable material like Custom Magic Items or the Item Familiar feat are not amongst those gamers, in my opinion.
And I am aware that there are other ways to pump skills. There's the divine spell Divine Insight, but that takes a Standard action to cast. They are wasting their first turn to get +8 (if they are using it from a wand) to their next Truespeak check. Inspire Competence only provides a +2 Competence bonus, not much. And a Factotum can only boost their Truespeak check 1/day. I'm taking precautions to make it so these options are viable, but somewhat impractical to rely on.
This would also actually allow Factotums a better access to Truespeak, since you can give them class features that emulate it, instead of requiring that they spend skill points.
The Factotum can't emulate SLAs, only Ex abilities. There's a feat they can take to get Utterances, and they all ready have Truespeak as a class skill (just like Iajutsu Focus). They merely need to invest the proper resources into the ability in order to be decent at it.
Which is another problem with using skills: why does your class require that you spend skill points to function? No other (base) class does that, does it?
Artificer. Need I say more?
Wouldn't you be just as well off giving a class feature that emulates skills but doesn't take up skill points?
Replace the Truenamer with the Artificer, then ask this question about it.
The answer would look something like Incarnum if you took the time to really
think it through (I mean serious amounts of 6 degrees of seperation here). Only a lot more broken.
This was the progression of reasoning for the Avatar fix to the fix. It started off as a skill. Problems arose of "hey this isn't a unique thing for the classes anymore, it's just an area where they were better", not that any other class could actually DO anything with a high check, but still.
I understand this. I'm selectively ignoring that part while making this fix. Think about how many classes have something that they are supposed to be good at, but others can do better in. There's too many to name, simply because of the sheer size of 3.5 in general.
In a way, both Incarnum and Martial Adepts have a similar problem. Feats can grant any character the same abilities they have. True they have unique class features that make them better than the others (save the Soulborn), and they are vastly superior at using those abilities than someone who spends the feats, but those abilities are no longer unique to the classes that they were made for.
Any Fighter can spend 8 of his feats to take Martial Study and Stance a bunch of times and get a ton of various abilities for it, just like anyone else can. But he won't be as good as the Warblade is with them, or anywhere near as versatile. Will he? Anyone can take Truespeech Training and the Minor Utterance feat half-a-dozen times to have a few tricks up their sleeves, but will they be as effective as an actual Truenamer?
I highly doubt it. They can get a bunch of 1st level utterances from each Lexicon, and at least one 2nd level utterance from the Evolving Mind (maybe more if they take Bonus Utterances at that point). But the best they can do doesn't compare to the real deal. They can get Word of Nurturing and Percieve the Unseen, but they will never have access to Profane Command or Invert the Sky.
And the fact that it is not really a good thing to require characters be built a certain way to even function (spend skill points). The answer was to give all benders +1 skill point per level that had to be spent on the bending skill of that class. And it should be obvious what the next step was here.
That's just it; my Truenamer fix never has to
spend the skill points to use their abilities. They can still buff the entire party or polymorph the Fighter into a killing machine. They won't be as strong without the ranks, but they can still provide for the party (their CL would be stuck as -3, but they aren't as reliant on it as other buffers are).
IE: A 17th level Truenamer with 0 ranks in Truespeak decides to hit the party's tank with Voice of Change. His Int mod is +10, so if he rolls decent (12 or higher), the party's tank just turned into an Iron Golem, or something (I haven't decided what the benefits would be). The duration? 5 Rounds, long enough to get him through the fight.
But let's say he failed the check due to not having a high Int modifier (let's just say he's focusing on the wrong stat). The party's tank would effectively be turned into a Troglodyte, thus gaining a huge NA bonus while retaining his equipment. The duration? Still 5 rounds.
What does not having the ranks mean? It means you can't get through SR very effectively, that's it. See where I'm going with this?