League of Legends: ARAM edition

[Geminex]

I know that LoL has no form of magic immunity whatsoever, that it doesn't have the same kind of roles as DotA and some are downplayed - lot less junglers, jungling is a lot harder, can't have a support that heals or helps with denying since no such thing as denying, getting rid of the notion of caster heroes who are strong early game but can't keep up by having skill damage scale...

Couple of things.
First, magic immunity is incremental. You can build resistance to magic damage (MR) just like you can build resistance to physical damage (Armor). This adds a good bit of depth to the game, I feel, as the damage enemy casters deal to you isn't necessarily straight and true, instead letting you negate a significant amount of it.

The fact that your enemies' resistance to magic scales with gold also means that many caster heroes are totally early game. A prime example of this would be leblanc, a burst caster with very strong base values, but who falls off later on because she doesn't scale with gold so well. She scales with gold a little, but casters generally scale worse with gold than autoattackers. So no, there are quite a few casters who are strong early, but fall off late.

Healing supports are totally a thing, sustain is one of the many things that make your support valuable. See champs like Sona, Soraka, Kayle, Nidalee, all very popular and useful. Particularly Sona. Generally you will also want some degree of crowd control (like slows or stuns) on a support to allow your carry to go aggressive, but saying that supports can't heal is patently false.

There's no denying, that's true, but I played DoTA, and I honestly always hated denying. Lets experienced players shut down newbies far too easily, and slows down gameplay. If you wanna deny your enemy gold and EXP, play aggressive and zone him. Much more interesting. This is also what aggressive supports do, they help you get an edge in lane and force your enemy to have to get past them every time they want to lasthit. There's room for a lot of variety in what the support does, overall, long as it helps their carry. Some pro teams have taken to playing burst casters as supports, just to be able to put on that much more pressure.

And as someone who plays jungler, jungling is perfectly feasible and a hugely important role in the game. Junglers are the one mobile role, and a lot of games are decided simply by how well the jungler uses his time. The creep camps are a bit tough at early levels, but that's no end of the world if you bring the right setup re: runes and masteries.

Anyway.

I used to play DoTA and liked it very much. Now I play LoL and enjoy it as well. I am not trying to claim that one's better than the other, here.

But given that much of what you're saying about LoL is pretty much entirely false, maybe you should do some reading up on the game before actually talking about it?