Hi Demetres,
Yeah, I'm with you; it seems like it would be worthwhile to try changing out the charging board. Since it is charging wirelessly, that tells you that the internal charging circuitry is working, at least as far as the wireless circuit is concerned. While not definitive, it is a good sign that charging works on the motherboard.
Replacing the charging board is really the only repair possible in this case; if there's anything else wrong with it, it's on the motherboard and that repair is far beyond what us home do-it-yourselfers can accomplish; in fact, it requires specialized microsoldering expertise and equipment to fix.
It seems like an issue of less importance to you, but the earpiece speaker is replaceable. If you buy the full assembly, you'll lose Face ID, but if you can solder and unsolder just two small points, the speaker itself can be replaced without losing Face ID. I wrote a guide for that for the iPhone X, but the steps are virtually identical for the 12. I can give you more details on that if you like.