Is lack of version number really a flaw of BIP39?

It seemed that BIP39 was often criticized as it lacks version number. However, wasn’t BIP39 supposed to be universal, that “one single seed covers all purposes, one single seed backups everything”? For example, Trezor supports multiple coins/accounts, as well as multiple address types (P2PKH/P2SH-P2WPKH), with only one single BIP39 mnemonic phrase. Trezor users can switch…