I am somewhat surprised by the statements about asymmetric crypto algorithms. Given a good library they don't seem more error prone and given many common use-cases they are not significantly slower.
(Incidentally ECDSA really is that much slower, but I appreciate that could be seen as cherry picking because ECDSA is slow even for an asymmetric algorithm.)
I don’t think the argument we’re trying to make is that asymmetric crypto definitionally can’t work. I’m pretty happy TLS exists. Just skeptical that you want to build your s2s auth on it.