Yes, but the abilities and item actives are all quite similar in broad categories -- dash, stun, slow, etc. Same with items -- broad categories of damage, magic, health, armor, etc.

To OP's point, you don't have to know the entire 100 hero roster and all of their abilities to have fun, just the general things they can do "Oh I just got stunned by that ability, might want to dodge next time"...

Obviously to be good you need to know them all, but not to get started and have fun at lower levels of play.