Specific classes give bonus skill training to specific skills related to that class. Yeah, they left that in there. Knight~> cant use magic/alchemy therefore combat skills get used more, which results in more skill training. It wasn't as specific but...
However, since the restrictions are gone the counter-weight is gone...and the classes have to be balanced around hybrids. What that inevitably means is that a pure build will always be weaker since a hybrid has everything a pure build has and then some.
how are pure builds weak?
if you are talking about mage pure build, then they are designed to be weak in the beginning and strong like zyrus in the end.
in mabi before the class system, pure builds are actually stronger than hybrids with the same amount of ap since pure builds focus on the type of attack.
which build would be stronger? a hybrid one where a person has r1 wm, r1 range, and r1 magnum or a pure one where a person has r1 wm, r1 combat, and r1 smash?
also hybrids becoming stronger because the pure build already maxed all its skills for the build doesn't count since the hybrid build would use more ap and that won't be a fair comparison.
Zyrus can't do anything without time to cast his spells. If he ends up in a situation where monsters multi-aggro faster than he can charge he's screwed. Magic is still very powerful though so usually it should work out. It doesn't change the fact that he's situationally quite limited and can be faced with many challenges (Lezzaro G10, small, quick-aggro rooms, elemental mobs, shortage of mp) that place him at a severe disadvantage.
A pure melee has an even tougher time since the only chance they have against multi-aggro is windmill...which costs them a good deal of hp. If the mobs are beefy enough to survive a crit-mill then you're instantly in a situation where death lurks just around the corner. Of course, pet play helps a ton, but even then you have to have several pets on call and have no room for error. You also can't tank worth anything and likely can't deal enough dps since you won't be able to smash.
A pure archer...well, I don't think I need to go into that. Miss, splat...that's about it. It's a high-risk style since you either effortlessly defeat all enemies or get your face smashed in by one. There's no method of handling multi either so if the monsters don't die fast enough things go south fast. This is why you'll see archers making heavy use of mana shield, barrier spikes and windmill to supplement their skills.
Inevitably in any system where different stats affect different damages pure builds will be stronger early on and hybrids will eventually eclipse them. In mabi, most people pick a few skills and focus on them then branch out later..and for good reason. Dedication pays off early on. The problem is that once you've capped your skillset you have no choice but to become hybrid to increase your power. Because of that the only viable endgame build is in fact, hybrid. What the old class system would have done is provided an option for someone to continue to grow stronger in their fighting style of choice while hybrids would grow stronger across the board.
Anyone who hybridizes from lvl 1is just executing poorly.
I fully believe the classes could have been balanced to the point where neither pure nor hybrid builds had a significant power gap over the other. The pure path would of course be better in it's respective area than hybrids and at a heavy cost, but since the skills weren't available to be strung in combos they could be more powerful without offsetting balance. The restrictions prevented border cases such as barrier spikes -> Hailstorm or charge -> Frozen blast -> Hailstorm which would have been too powerful.
This new system facilitates specialization at low lvls which will probably be helpful to new players...but beyond that it only accelerates the path to hybridization. Anyone who wishes to stick to one style of combat has to accept being weaker than everyone else. There's still some potential to it depending on what kind of boosts they give...but since skills aren't restricted they will inevitably have to be less powerful.