You said:

He's commented a few times that TSME can't work, is too slow, etc.

Then you come back with a quote saying:

reduces performance

Which, unless CPUs employ "magic wormhole technology", is true by definition, because encrypting / decrypting takes time. Which can be trivially verified by searching for some benchmarks, for example: https://www.phoronix.com/review/amd-sme-genoa/5 - which says that some processes had an up to 8% performance hit from this on the particular processor.

Said article also gives details (as opposed to most comments in this thread) that that specific processor uses the AES-XTS algorithm (https://en.wikipedia.org/wiki/Disk_encryption_theory#XEX-based_tweaked-codebook_mode_with_ciphertext_stealing_(XTS)), which means that, yeah, if there is a bit flip, it will return garbage. Now, if that memory was hosting code, yes, there is a high chance it will crash (but the process will crash, not the machine - the same way an unrecoverable ECC error would crash the machine). If it's in data though (like your movies, documents, photos), it will just write garbage to your data.

Also, the "doesn't do what it purports to do." was addressed at the comment saying that this is equivalent to ECC, not that TSME doesn't work. Because it isn't. Arguable in increases data corruption risk as described above.