Dota 2 can be played in a variety of ways, even if the goal is eventually the same. It's not unlike how you can approach a project from different sides, all of which push to the eventual goal of its completion. It doesn't make the game less fun or more predictable.
As for champions of LoL, it's twofold. First, it's a paradigm change from the original DotA from WarCraft III. That, in itself, would cause a lot of uproar, empty and meaningless as it may be.
However, it's the second part that brings the argument up for me.
In Dota (both the original and the standalone) all players start out equally, barring skill level. Each player can pick a hero to either enhance their team's performance or counter the other teams' enhancements. What use, say, your illusion-based hero against one whose spells increase in damage based on how many enemies they hit? On the other hand, while you can't counter strong pushers directly, you're likely to be able to harm their farm or ability to take part in pushes with certain picks.
It's the same foundation, the same base for everybody that does it.
Having all heroes available to you from the start has been the founding principles of MOBAs. You can play whomever, and while there are certain more prevalents ways to play certain heroes, nothing is stopping you from changing your style for this match or even this hero. The fact that you have to earn your champions sounds like a false achievement when everybody else's characters are there to be picked from the start. Know what I mean? Couple that with the fact that you could pay real money for that, and for many non-native players, it crashes the experience.
You're right to note that Dota 2 is a more skill-based game. You have to know your heroes, your items and even your map to navigate your game and be able to push it to victory. I'm not gonna deny its steep learning curve: I'm still learning things about the game, although now it's ways to use all the present things I know about rather than anything new. Who knew you can save your squishy support with an astonishingly-powerful ultimate by hiding it with invisibility cloak? Everything but area-of-effect disables are off the shelf for those precious few seconds.
I'm not against LoL or people playing it. If that's your thing, that's your thing, and I'm not gonna judge you for that. I've seen people switch from LoL to Dota 2 because latter is more complex. I've seen LoL players try Dota 2 and not get it. I don't like the superiority complex Dota players gain nowadays, but it is a more complex and it does take more skill to play. Doesn't mean other games are inferior.
EDIT: Feel free to ask me about how different a hero can be played in Dota 2. I'll do my best to explain it using as plain language as possible.