all I can add to this "wrenching saga" besides congrats on prevailing and getting the cups out of your Swiss BB shell,
I once came to work on a genuine vintage Swiss bike with Georg Fisher sandcast BB shell (so 100% was Swiss threading) that PO had installed a BSC (British/ISO) sealed BB unit into those Swiss threads. Alarmed at first I expected full tragic buggery but got the sealed unit out without any major struggle, maybe all due to it having alloy cups on both ends. Plus the BB threads in that Fisher shell did not appear much bodgered either and Swiss cups (actually Phil Wood Swiss steel "rings") could screw in and were "tight" but manageable.

as always with such "mix and match" experiments, YMMV