The CGI in Spider Man Homecoming was pretty pathetic as well. Isn't it just a case of Marvel not giving a shit about CG effects? Why waste money when the movies are aimed at manchildren who would go see it regardless?
What you ought to know is that the VFX inflation in current film has been dramatic. I don't have an exact figure but in Marvel films you can probably assume that half or 2/3 thirds of the shots, if not more, have had some VFX work. There's tons and tons of invisible stuff everywhere (like in Homecoming, Parker is in a deli or grocery corner shop, half of it -aisles, labels, decoration, props...- has been composited in post) on top of the most complex work, and the latter often requires an obscene amount of rotoscoping (which is very manhour intensive).
I don't think they really cheapen on VFX (aside from extorting the lowest prices from the contractors), it's just that expensive to get everything done in time to stay within their schedules. It's only the most complex work (animating lifeforms and humans, in short) that sometimes isn't up to par and that's expected really.