Though this comes with it a second lesson, not in what is done but what is not done: The risk of shallow experiences which do not grip you.
A very long (non-ranked) LoL match takes 45 minutes to an hour. A short one can be as little as 20 minutes if the enemy team performs particularly poorly (whether through bad luck, bad plays, or bad behavior). With such a narrow time window and rapid game turnover, you need characters that are easy to get into and easy to get out of. D&D doesn't work like that. Indeed, I would argue it can't, and trying to make it so would break it.
I've been playing more LoL casually lately, as I've met some folks who play, and a champion I like aesthetically (Aurelion Sol) semi-recently got a rework. His old design was...clunky at best, very unintuitive, and not particularly rewarding even if you played it well. The new version, while losing the One Weird Trick that he previously had, is significantly better, and in fact one of my favorite champions to play. (I like scaling champs, and Aurelion Sol is neat because he doesn't just scale for damage, he also scales for area and range, which really matters as games wear on!) He became much more standard, much easier to slide right into--much less to catch on, so to speak.
But that process cuts both ways. There's nothing to hold on to later. No depth and little complexity. 90% of games, you'll buy the same items, and only swap out 1-2 depending on the context. You'll always have the exact same suite of abilities. This, again, is good--great, even!--within the context of LoL, where matches are meant to be relatively short.
In the contest of D&D, where even for very old-school-minded players a single character should last several weeks if not multiple months of once-a-week, multi-hour sessions...having nothing to catch on can be a pretty big problem. People slide in...and the slide right back out again, having gained little to nothing from the experience. Finding the way to balance these two concerns--making it easy to get in, but also easy to get hooked, to stick with it, to feel rewarded for doing so--is an extremely tricky design problem.
This is why I talk as much as I do about how "approachable" a game is (how easy it is to get into the game) and how much "depth" it has (how it leverages its parts to provide an engaging experience.) Different players want different amounts of engagement--what is just right for one player may be stultifyingly boring for another and vastly too complex for a third. The lesson to take from MOBAs is not that every character should be dirt-simple so that it can be fully explored in 25-45 minutes; it's that every game should focus on upping approachability while preserving a selection of different options for depth.