What standard are you aiming for?
The standard I'd use for revising feats is "a PC could pick this at level 4 and build an effective character concept around it".
Elven Accuracy, Polearm Mastery, Crossbow Expert, Lucky, Sentinel, War Caster, Svirfneblin Magic, Magic Initiate are examples of ones that currently qualify.
Too strong means something that breaks things (a) more than the above, (b) possibly as taken at level 1.
(GWM/SS are strong feats, but mainly come online around level 8, after you have near-maxed your attack stat and already grabbed XBE/PAM).
Your changes make HAM start to approach this. It still scales poorly. My variant is "you reduce BPS by your proficiency modifier. Unless you are wearing magical heavy armor, this only applies to non-magical BPS." This weakens HAM at level 1 (where I think it is too strong), but makes it scale much better (so you won't feel bad about it at level 20).
Elemental Adept as written just lets you build a character who is "all fire all the time", which isn't a bad thing. But I don't like the idea of burning fire elementals. So one approach I am going to try is:
Elemental Corruption: You have twisted your elemental magic to make it more effective.
- When you gain this feat, choose one of the following damage types: acid, cold, fire, lightning, or thunder.
- Spells you cast ignore resistance to damage of the chosen type.
- When you deal damage with a spell of that type, you may choose to make 1/2 of the damage necrotic. If you do so, you gain temporary HP equal to the necrotic damage done to one target until the end of your next turn.
- If you have temporary HP granted by this feat at the start of your turn, you can sacrifice them in order to increase the damage one spell that deals the chosen type of damage on one target on your turn by half the sacrificed temporary HP.
This is basically a dresden-files esque "hellfire" upgrade.
Against a creature immune to fire, you can use your corrupt flames, and they still take 1/2 damage as necrotic.
When you use your corrupt flames, you drain life power (temporary HP), which you can then expel to deal more damage.
This isn't as "neutral" as elemental adept is, and is honestly too complex, but it does give a fire-wizard something to do when enemies are fire elementals. That energy substitution (fire->necrotic) is a lot like treating immunity as resistance, DPR wise.