Any class can do any role-- Healing, tanking, Magic DPS, stamina DPS. Stamina sorcs, for example (while in a rough spot at the moment) can be just fine- it seems like a weird concept at first (why would a sorcerer whack people with a giant club?) but the way the game is designed means every class can do anything.
"Hybrid" in ESO is generally used to refer to a build that uses a lot of both stamina and magicka. Because damage scales off max resource, splitting your attributes between the two gimps your damage. If you're planning on playing a stamina sorcerer, for example, you'd ignore most of the classic "sorcerer" abilities and build lots of stamina and stamina regeneration and use stamina skills to do damage, while buffing yourself with magicka skills.

Because of this huge variety in what each class can do, there's no "best" skill or armor or weapon for any class. Builds vary massively between people and while there may be a theoretical "optimal" item and skill combo for DPS for a given race/class combo there's a lot of debate by the masters of each class over what that best build is.

As for how each class plays in the end game, there's so much variability in what each class can do that the question is hard to answer. Many DPS builds will play the same (buffs, DOTs, spammable, repeat) but that would be completely different from how you might play a healer of the same class (HOTs, team buffs, team resource generation, damage, be ready to burst heal) or from tanks (taunt important enemies, keep buffs up, block important attacks). Even among different DPS styles your rotations will be different, and some healers are more DPS than healer and some tanks focus so hard on damage and self-healing that they fall into a totally different category called sap-tanks. It all depends on how you want to play because you can do literally any role with any class