Well different heroes doesn't mean you can't make comparisons between the games, there's no heroes like invoker or meepo in either lol yet you can compare them and there's no heroes like akali and ezreal in dota but you can still compare the games. It's a good thing they have original heroes, otherwise it'd show pretty fucking awful design.
I don't know about wow bgs, it still has the general overarching concept of 2 bases, destroy the enemy base to win. Secondary objectives while similar to BGs, are just that, secondary, you can win a game without ever touching any of the other objectives. It's just different objectives, nothing much more to it, it replaces roshan/nashor/dragon/blue-red buffs concepts by having dynamicly spawned objectives that are also map specific. Customization isn't very far off even with the current fairly low number of talents on most heroes, since talents do change stuff enough that they're very similar to large item upgrades, without having to farm for them(which is both a bad and good thing, which you weight more than the other depends on people). Mostly the key difference is level sharing and removal of secondary ressources in favor of only xp as form of progression and shorter games due to faster growth and reduction of the early game to only a couple of minutes.
It's still closer to dota/lol than to wow bgs I'd say, because of the base centric gameplay and gameplay mechanics(how CC interact, how skills are designed, point of view obviously and such).