lol you're right here and I think I may have forgotten to mention that. Regardless, I don't think DsO or Ildjarn are schlepping some image per say and neither could be labeled anything other than BM despite offering very different sounding material. I'm not trying to be some gatekeeper here though I admittedly listen to a lot more BM than Thrash. I guess this all just boils down to what you said considering the scope of the two genres as frameworks. It's insane to see the how many bands are retroactively being labeled as BM despite the 2nd wave having no awareness of their existence.
Ultimately, I respect and acknowledge that Thrash has mostly steered away from too many gimmicks and relies more on musical chops, but is that at the expense of stagnation or is stagnation its trademark like most modern punk music? It's clear that Thrash did indeed evolve in the 80s, but in the form of bands like Possessed and Celtic Frost. I don't think modern Thrash can be anything but revivalism and that's fine. No one is seeking newer Thrash bands in the hopes of finding anything but RIFFS anyway.
I'm also not sure why aesthetic has to equal image exactly. Sure a lot BM are steeped in juvenile lore and edgy posturing, but there are plenty of bands that set themselves apart with songwriting like Panphage vs. Malokarpatan. I think you're just cherry-picking memes about the genre without seriously considering that the sound just isn't as pigeonholed as Thrash. I'm not trying to argue that one is better than the other.
edit: im p hammered so excuse the flight of ideas
Thrash evolved in many ways beyond simply paving the way for extreme metal. Megadeth, Dark Angel, Prong, Coroner, Pantera, Voivod, Anacrusis, Fear of God, Meshuggah, Stone, Nevermore, Depressive Age, Mekong Delta, etc all had plenty to say and do differently from one another. The thrash bands died largely due to lack of label support more than there simply being no further room to push things.
I don't know why you keep shitting on punk music either, which is without a doubt one of the most diverse and creative forms of rock music. Black metal itself was basically predated by hardcore like Charged GBH and post-hardcore/noise rock like Blind Idiot God and Ham. As far as I'm aware, there are still bands pushing the envelopes of punk's many children and grandchildren. Black metal wishes it had anywhere near the breadth of punk music.
Malokarpatan is retro-heavy/speed metal based on their new album, probably 15% black metal at most. Not familiar with that other one, but outside of dissonancecore stuff like DsO (which arguably has more in common with Immolation/Ulcerate/Gorguts than Burzum or Emperor), black metal hasn't shown any musical progression over the last couple decades afaik. All the essential tropes were established in Norway in the early 90s, mostly by just Mayhem themselves. You're right that the sound isn't as pigeonholed, but only because it's black metal fans that do the pigeonholing. Meshuggah writes songs with one riff? Totally not even metal, let alone thrash! Wold writes songs with one riff (or less)? Ambient noise black metal brah.