Per the Players’ Companion, if a character class has enough levels of Thrassian, their effective amount of Fight in the class is increased by 1 or even 2.
This means a character can have Fight 3 or Fight 4.
Question 1) Do characters with these higher levels of Fight get their proficiencies and damage bonuses faster? These abilities seem to be tied to saving and attack throw progression.
Question 2) Would a human Custom Class that is HD 1, Fight 3 (not sure what to call it), so reaching the 4 build points, be unbalanced?
For my two cents, I think it balances out. I did a version of the Duelist using that same concept. I need to go back and tweak it because I forgot to include the proficiences (I had just gotten the Players Companion and wanted to fiddle with it).
My only suggestion is that when making it, tweak it a bit more with a few custom powers to further differentiate it from the fighter. I know some aren’t wild about the option because it makes the fighter no longer best at his role. Also why I suggest you tweak it a little to not step on the fighter’s toes.
The class wouldn’t get saving throws or proficiencies “faster” in any way, per page 81 of PC “If the rating for one category is highest, use the Saving Throw progression for the core class which is associated with that category” They’d have the exact same throws as fighters.
Same goes for damage bonus, per table on page 78 of PC. That’s where all that information is located. They get it every three levels just like a fighter would. The only advantage of fighting values past 2 is better attack throws.
I don’t think it would come out unbalanced - that d6 hit die is penalty enough - but I would say that you’d want to do some tradeoffs so that you have a class that’s interestingly different than a fighter.