Bumper got a spotlight in a couple of issues of the Dreamwave Ongoing and popped up in Megatron Origins. I think that means he had more appearances and lines of dialogue in (western) TF fiction than Hub Cap's ever got.

The recent Soundwave spotlight in RID was good at fleshing him out, so much more so than the actual Spotlight Soundwave comic!

One problem I have with MTMTE (and I have very few) is that the characters, while great, sometimes don't reflect the G1 bios at all - or if they do it's at a very long stretch. And sometimes that's because of other factors, like when they swapped Powerglide out and Tailgate in, Tailgate picked up the habit of exaggerating his role on pre-Ark Cybertron which would have fit Powerglide better. In some cases they may as well be new robots entirely. I woudnt mind a few more little nods to their G1 bios showing up.