It's a lot more casual in some aspects, because they removed a lot of things from Dota - no deny mechanic, limited creep blocking, no creep pulling, no jungle stacking, jungles don't cycle random camps, towers actually deal punishing damage (it hits harder the more it hits you), simplified micromanaging, an actual distinction between lanes and the meta, no soloing the huge monster at low levels (heck probably only sion can solo baron at all even at max level), no money loss upon death, a smaller exp curve to ensure no huge gaps (wth I'm only level 15 and the enemy antimage is level 25? OP!), the enemy carry is actually squishy in contrast to dota carries which get really tanky the more items they get, etc etc.
tl;dr League of Legends is a more simple Action-RTS than Dota is. That's not to say I don't enjoy the latter, but I feel like there's way too many variables to put in for a casual like me to have short term fun.
Ah, now I understand what you mean, and it's true. Usually after a game has existed for as long as DOTA had, the harder it is for a newcomer or casual player to play for fun considering how it becomes more geared toward competitiveness. A person doesn't need to play the game itself to know the trendline.
Now game mechanics aside, Towers actually work in League of Legends? That's... very very rare. They're usually just for support and get crushed easilly in a wave.