Hussar
Legend
Compared to what? Compared to point buy? Compared to what? Relative to any other game system I've ever played - including Amber for crying out loud - a class system most certainly does encourage the opposite of specialization.
Classes encourage generalization? Buh?
Take a wizard. Arguably one of the most powerful classes in the game. Give him Martial Weapon Proficiency Longsword and then take your next three feats in Armor Proficiency. Give him a longsword and full plate. How effective is he? Short answer, he's not. He's tried to step out of his niche (caster) and into another (tank) and he sucks hard at both.
Even if you give him levels in fighter, he still will suck if you try to put him in armor. The ACP just kill his abilities. You can end run around that by taking the Still Spell feat, but, now all his spells are one level higher. Or, you could drastically limit his spell selection to only take non-somatic spells. However, he still has very bad hp's compared to a fighter and a poor attack bonus. So, he's a crap wizard and a crap fighter.
If you want to make an effective tank, adding levels of rogue is not the way to go. If you want to make a smooth talking con artist, fighter is pretty much out the window. The list goes on and on and on. Splitting your role makes you less effective.
In skill based systems like GURPS, I can make a decent face man with combat skills and medic skills. Depending on the starting point buy, I could add even more. Later on, as we gain experience, I can continue to broaden my repertoire without losing out on power since most challenges are fairly static. There is very little scaling with levels.
Because of the scaling in D&D, generic characters get left behind very, very badly.