I'm mostly against the idea of outright nerfs for any character. I think that the balance of power in any tier could be shifted by aiming to create characters that share equivalent power and designing towards a rock/paper/scissors style metagame. So I think all of the following characters could use a "buff" or at least be reworked in such a way that they could be considered team picks that either support or disrupt the tier's meta.
3* Tier
Hulk, Doc Ock, Ragnarok
The 3* meta is quite foreign to me now, although I'm assuming that not much has changed since the introduction of Strange and Thanos anyway. Hulk was any easy pick, his abilities really are a bit of a mess. The remaining picks were simply two characters that I feel are fairly close to the bottom of the tier and just have powers that are uninteresting or otherwise surpassed by someone else in the tier.
4* Tier
Kingpin, Wolverine, Sam Wilson
Fairly easy picks for me here. I think I'm actually pretty happy with all the other 4* characters right now. KP and Wolvie both received bad reworks and Sam was obsoleted by Carol.
5* Tier
Doc Ock, Hulk (Banner), Spider-Man (Back in Black)
Also easy picks. The doctors Otto and Bruce both need some attention. Spider-Man is probably an outside pick, since I know most people would prefer to see Logan at least somewhat restored. Black Suit Spidey is there because he's simply been taken out of contention by the fact that he shares a name with Peter Parker. I think that they could probably rename this Spider-Man to Venom and keep the abilities intact (at least until after they fix OML).