Essentially you don’t get killed in combos by…(and I know it sounds like I’m being a smartass) learning to play.
That is literally the only way you won’t get destroyed in this game.
As far as online play goes, well… if you want skill to mean something, then just don’t bother with it. Quite frankly this isn’t the kind of game where even a hint of lag is just “ok,” and online Marvel is, in my experience, always laggy to some degree. Certainly enough to toss the concept of “skill” out of the window. The only consistent thing online is spamming (and I do mean spamming, not zoning, even zoning tends to fail against all out spamming). I’ve even managed to beat the likes of Dios X online. A feat which I assure you, offline, would probably never actually happen.
There are some people who are literally two different players online and offline. Myself included. I’ve racked up almost 160 hours of offline play, but if you play against my 6 hours of online play you’d probably very well think I had only had the game for a couple of days at best. Unless I’m trolling, in which case I can spam like no other lol.
So just practice, get better, learn the game, and make sure that you can hold your own offline. It’s cool to hop online just to dick around, but the moment you begin trying to use online gameplay as a measurement of well… pretty much anything, you’re going to either wind up hating Marvel or having a severely skewed sense of “how” to actually play.
If you’re in an area that has a “scene” for Marvel or are able to travel to an area that does, then do that. Hell, even get a couple of local friends into the game to play against. Don’t worry about online prowess unless you absolutely have to, because no matter how good you get at it you’ll always be one poorly-timed lag spike away from getting destroyed.
Furthermore, being able to mash out of combos is just about the most skill-less concept that could possibly be implemented into a fighting game, so someone concerned with skill shouldn’t be wishing for such silliness.