those are not legacy. All those addresses are post-fork.
legacy addresses start with 1

I always assumed there was a technical or economical reason all multisig I've encountered so far seemed to use "3xxx" nested segwit (instead of native segwit or Taproot)

is that not the case?

Then again I haven't rabbitholed into multisig proper yet

nichro

if somebody still use a legacy address, it means they didn't even got doubled their BTC stash in the 2017 fork... LOL such losers.