No idea why this is upvoted. I was ~5.8k mmr on Dota (only played for a few months) and Master's on League.
Firstly, runes and masteries. You should be more direct in your answer, OP, runes and masteries scare away most players. Guess what? 99% of players/pros use the same/very similar runes and masteries on every champion. Use probuilds.net to see what I mean, they are not as scary as you think! It's basically just more base stats for your champion, and you basically know 100% what everyone is going to use with some slight changes.
Item builds are absolutely not more in depth. That's complete hog wash. When I was learning Dota 2 I was confused as all hell what to buy. Pros would build different items on the same champion every damn game I obs'd. Of course if you are pub stomping it's the same, but for high mmr/pro play helllllll no. Dota builds are so insanely situational. On League, it would be easy to give you a fits all build with some slight variations(i.e. when to buy armor vs mr) for any champion in the game. Again, probuilds.net to get an idea of item builds. You will see every pro builds similarly on every champion despite what this guy says.
LANING IS SIMILAR? LOL? Not even close. Exp is way different, level advantages on League means way more, ganks are 1000x more scary on Dota, I could go on for days about how different it is. This will be the hardest part for you OP, learning to lane takes PRACTICE. You will not be able to get a good answer here. Laning is akin to the game itself, it is a lot different compared to Dota. Your gold, creep management, towers, ganking paths, lack of item shops/tp/chicken, exp gains in duo lanes, no creep blocking, no up hill advantage, NO DENYING, no denying towers, etc... I could go on for DAYS. There's SO many things which are vastly different.If you lose lane on LoL it means you will be poked under tower and have to recall and lose more CS. On LoL there's no creep aggro tricks like on Dota and you can literally basically auto people 24/7 in creep waves since creeps are slow, you can drop the aggro. Of course they will still focus you. Again - practice! You will quickly see how different the games are.
Power spikes exist in both games, no real difference. I'd say Dota power spikes are more impactful in a lot of cases, as some items are insanely overpowered such as blink dagger or bkb. The thing with League is there's always a dragon to fight for, so casters tend to speak about power spikes since you know 100% a 5v5 will happen unless one team gives up dragon for free. Fighting around a power spike as a TEAM is a thing on League, on Dota it's more like, oh let's buy blink and kill someone for free.