Someone said:
Ok, I'll try to make it simpler. Is or is not true that many prestige classes offer objectively better benefits, once you've met the requisites than continuing adquiring levels in the base class?
Well, allow me to jump in and get flamed
Someone, the problem I see with yoru argument is that you are looking at whatthe calss gets when compared to a straight archtypical charcter of the same general abilities. Radiant Servant--CLeric etc. While that is one way to compare, I think you need to take more into account, namely the prerequisites of that prestige class, and what it has cost you versus the benefits of the standard class.
How about archmage, which you brought up.
Spell focus (2 schools)
Skill Focus (Spellcraft)
15 ranks in spellcraft and Know-Arcane.
One feat you would have gotten from 5 wizard levels
So we have three weak feats and the 15 ranks is heavy, but arguable. Personally I rarely go that high, and tend to top out at about 10+ modifiers.
YMMV, but I consider this four wasted feats and 10 wasted skill points to enter the class.
In return you get normal BAB, HP, skills and Saves, so no problem or benefit there.
And you get five special abilities. Spell power is not very good, so let's look at Mastery of Energy, Mastery of Shaping and the Spell-like abilities.
Mastery of energy is nice, maybe even great. But bythis level the Wizard's best spells have nothing to do with hit point damage anyway, or are force/disintigration realted anyway. Generally I have found that with Energy Sub:Sonic, I have no real problems with energy resistances, and if I go fire with Searing Heat from Sandstorm, I can laugh at Fire resistance, and even immunity is not too bad.
But for argument I will say it is worth 1-1.5 feats.
Mastery of Shaping is even better, espeically if you are a blaster, and even for non blast spells like dismissal, or prismatic effects it is nice to be ableto ignore your allies. However, for a feat taken much earlier, you can do this for a modest level bump. But still 1.5 feats about?
Now spell-like abilities are tough as Wizards do not have many slots at all, anyway. Spendingthe 6th elvel slotto cast fireball 4 ties a day is not bad, but ponying up a 5th level slot(one of the most valuable in the gmae) really hurts.
So I would put each ability at roughly at .75 to 1 feat.
Compared this way, i would say it is balanced. Compared without prerequisites, it is of course far superior to 5 levels of wizard. One reason prestige classes like the Incantrix, with its laughable entry requirements AND bonus feats is too strong. I mean really, who would not take incantrix and complain about taking a metamagic feat? That is the purpose of the class.