"I want to turn into a powerful combat beast!" seems to be what you're defining as the goal of the player experience. (Please correct me if that's wrong.)
It is wrong, yes. Well, sort of.
I'm not talking full on ultra rage beast Crinos instantaneously. I'm talking...getting to rage in pretty much every fight, as opposed to only a third of the expected fights every day. Even in 5e, you get (at best, prior to literally level 20) only
most expected-by-design fights with an actual rage as a Barbarian. Because your rages per day top out at 6 prior to becoming unlimited at 20. Really? Raging, the thing you become a Barbarian
specifically for, is something you only get to do
half of the time for most characters, if you actually follow the encounter amounts expected by the designers?*
Or as I noted above, Bardic Inspiration is (for the vast majority of characters) only
three per day until you hit 5th level. Meaning, for 40% or more of the actually-played game, you barely get to use it.
Or consider how, because feats must compete with ASIs, you essentially
never want to take them before 8th level unless you can get them for free. And you're
massively incentivized to make that feat be one of the small handful of extremely powerful feats, because if it isn't one of those, you'd almost certainly get better results from just taking +2 to your prime stat.
That's the kind of place where even 5e, today, stumbles on the execution of the "let's support players actually getting to do/be what they want to do/be." And 3e was worse in essentially every way. Look at the example shifter PrC. First you have to already be a specific race, which has hefty penalties (-2 Cha and Int!) and by default only gets to do its special thing
once per day, and you must take at least one Shifter feat (most of which are mediocre at absolute best and frequently crap, but required so you can actually use your Shifter stuff to any reliable degree.) Second, you must have two specific skills at high rank
which only one physical-fighter class gets as class skills, that being Ranger, and you would never want to give up animal companion ranks and caster levels for it on that class, meaning this PrC is locked behind
ten or twelve levels of progression for most characters who would want it. Third, it requires BAB +4, meaning even for classes that do have both K(Nat) and Survival, you're probably waiting until at least character level 7 to get any of these benefits. Fourth, your only significant benefit prior to third level in the class is...a stat boost and one or two natural attacks. So if you have a fantasy of being a cool weretiger barbarian or whatever, better hope your game is going to hit...13th-15th level!
This is what I'm talking about when I say people have to "earn" their fun. This isn't "oh, the class is trying to avoid front loading." This is a situation where getting go do the cool thing you signed up for may take three quarters of the
maximum playable range of the character--and for many games, will simply lie completely out of reach unless otherwise noted. And you're going to have to sink half a dozen feats into it so you actually get to be a cool werewolf warrior often enough in the day to be worthwhile, because every fight that you don't use your Shift powers, the
entire PrC is pointless, worse than just being a bog standard Fighter.
Even the absolute most catered-to classes in 3.5e, like Wizard, Druid, and Cleric, have lesser shades of this "earn your fun" type design, where you'd better be ready to play for literally months or years before you're allowed to
sometimes do the cool thing you imagined as your core shtick.
TL;DR: I'm not talking about doing the ABSOLUTE MOST AMAZING SHOCKING DRAMATIC THINGS
EVAR!!! I'm talking about getting to do the
core "cool thing" that a class or race bills itself as offering, and getting to do that more than a piddly 2-3 times per day, e.g., getting to do it
most of the time, as your core shtick.
*Note: I 100% get and agree with the criticism that the "6-8 encounters per day" thing is foolish and based on erroneous understandings of how people actually play 5e and D&D generally, but the game should be evaluated on what it was designed to do, not what house-rules people place upon it.