From my experience DOTA is much harder than league. If you have trouble in both you might want to play league.
In DOTA you can turret dive much easier. In league, you are pretty “safe” behind your towers for the first 15 mins of the game.
In DOTA you can deny last hitting minions and towers. In league, you don’t have to worry about being unable to farm because the other player is better than you or gets ahead.
DOTA snowballs a lot harder and because of this you can carry your team a lot harder. In league, if you are really fed you might be able to 1v3, but most matches are pretty even.
In DOTA the abilites are much more powerful. The abilities in DOTA feel like ultimate abilities in league. DOTA feels cooler and looks nicer. League is just easier to play.
I’m plat in league and a complete scrub in DOTA. Probably a little biased too.
TL DR: DOTA too hard; League is much easier.