Skill build - What's the point?

[smartthegod]

If I'm right, in games builds are made so each player has free choice of spells and abilites they like to have, to make a difference between each player. Otherwise, there could be spells that everyone will have, so no point of having a skill tree. Why I'm saying this, is because there are too many skill points at lvl cap. How can it make a difference when each player has almost enough points to choose all spells and passives available?(Don't take it literally of course) I mean, each player has enough points to choose all most useful passives, plus some even have spare points for passives like speed, because there's no point in investing them in useless abilities or new skills when there's no use of them(because of 4 slots only). And what's gonna happen with new lvl caps? People are gonna put points even in damage passive lol, though they'll have no use of them(with dmg pets). That's why things should be changed before new caps. Or new skills that are not gonna be useless, or passives that reduce cooldowns, or passives that give say procs and probably there are even more choices. I think developers should learn why do skill trees exist.