Not to get caught in a your game sucks comparision, here are a few details I don't think have been expressed.
League champions are designed for a role, and constrained to it. This limits skill design, but speeds up learning. The gameplay is an on screen skill shot fest, where small pokes and trades/jukes yeild advantages. The map is smaller, and the mobility of champions is far more constrained by what happens in Dota. The league items are largely passive, rarely active.
The hero design lets them make you pay for the cast, because you've always got access to some of these fixed role heroes. Everything happens on screen, even the 5v5 teamfights
Dota heroes are designed to have skills or combinations of skills that are unique. The playerbase and the gameplay determines the roles that work best. A new player has 100% access to every aspect of Dota as a professional who plays at TI. Its skills, bindings, and keys are related to RTS controls more deeply than league. Dota skills have far more range, and a huge part of the game is vision and the abuse of what your opponent can see compared to yourself. Dota has a bit less spell spam than league, but its spell casts do massively - in a league context - broken things. The dota map is larger, and you can feasibly buy an inventory of active items. Which effectively doubles the hotkeys depending on build.
I much prefer the rock paper scissor of a Dota game, and the depth even if I suck at utilizing it. I enjoy access to the full cast and the power of spells. No supports in league have spells that would kill a pos 1 alone. With bad positioning, supports in Dota can. Mechanics like buyback, map size, and items create a very difficult to understand procession of how winning and losing happen, but if you focus on the fun and your own gameplay I enjoy it so much more.
League is a bit of a 5v5 top down arcade fighter, Dota is layer upon layer of skill and counter skill/item. I don't think one is better than the other. But I far prefer what dota offers in the end.
A great game in Dota or league is amazing. A bad game can be ball busting in either. Welcome to the genre.
To be a master of league, takes a lot of APM it is very much twitch. While fast fingers are rewarded in Dota, deliberate execution that takes many fewer total clicks can be explosive.
The strategy layer of Dota is deeper. Both games evolve over time. The rank list of best heroes in a patch is variable, which doesn't matter in dota because you can play anything you may just be terrible at it. Either game is a commitment to constant learning.
Dota has had numerous - amazing systems added in the last years. Talents, level 30, new items, neutral drops. Its in a very fun space in my view.
I have thousands of hours in dota, and probably 500 in league. You'd have to pay me to pick up league again.