

Is this even the worst he is publicly known to have done? The 2020 coup attempt and aiding the GRU in attacking domestic targets (both of which are outright treason) rank higher in my view, and would be slam-dunk convictions in any country with a functioning legal system and a modicum of democracy.

Some very good suggestions, and not just the already well-known stuff among mainstream audiences from most of the other comments.
I would personally cite Cocteau Twins over This Mortal Coil, not only did they predate them, but Treasure is also the better (and more influential) record in my opinion.
Therion has been quite explicit with its acknowledgment of Celtic Frost as a major influence (even taking the name) - though their records suffer from subpar production, and one could argue Therion was able to fulfill the ambition of Celtic Frost.
One shouldn’t mention no wave without mentioning Swans, who were massively influential to grunge, post-punk, post-rock and heavy music in general. The colossal Soundtracks for the Blind is their magnum opus.
Aside from Kraftwerk, the krautrock scene spawned several more highly influential groups, including Neu! (who invented the remix), CAN (cited as a major influence by Radiohead and many others) and Popul Vuh (pioneers of early ambient, electronic and “new age” music).
A few more suggestions not related to yours: Oddly enough Zappa hasn’t been mentioned yet in the comments (as of writing this comment), probably the most influential pop music artist of the 20th Century, though his music can be challenging at times and not all of his humour has aged very well. We’re Only In It For the Money is probably the best starting point.
Brian Eno - Apollo. Not Eno’s first ambient album, but probably his most accomplished one.
Talk Talk - Spirit of Eden. It’s hard to believe you are listening to what used to be a new wave band only a few years earlier if you play this record. It was so far ahead of its time their label dropped them amidst an acrimonious lawsuit.
Ulver has been cited as a major influence by modern electronic music artists (e.g., Carpenter Brut). Their output is extremely diverse and creatively shifts dramatically from album to album. I would recommend Perdition City as a starting point.
Godspeed You! Black Emperor - F#A#∞. Not coincidentally released shortly after Soundtracks for the Blind, a massive creative leap nonetheless and one of the defining post-rock records of the 1990s.