Yes, I agree with the telling vs showing criticism here. Interesting considering the use of flashbacks for exposition, that there was really none used for showing the Hank/Hope history, and the Hank/Darren history.
That said, the above, along with the Pym Particles head messing may NOT have been sloppy writing, but rather editing sacrifices. The kind usually made to satisfy producers short attention spans, and their projection of such onto audiences.
The Cross/Lang "conflict" was certainly not as inherently personal as the Pym/Cross conflict, I agree, but I think that, as others have said, the jealousy/projection aspect is a valid, and satisfying, character conflict for Cross and Lang for me.
Then, of course, Cross making it personal for Lang when he goes after his daughter.
Not as much depth, I guess, as they could get from what they had (but didn't go so far to show) with the Pym and Cross history, but it was satisfying none the less.
Over all, I found the movie to be strong enough, and entertaining enough, on it's own, that it was not cut down by not exploring some character avenues as well as they could have/should have. Especially considering the film's production history, and the likely hood of final edit compromises.