I think it is faster to validate the checksum than it is to check if the phrase generates a known address.
It's much faster. The checksum is a single SHA256, while to generate an address you need 2048 rounds of HMAC-SHA512, a variable number of further rounds of HMAC-SHA512 alongside elliptic curve multiplication to work down the derivation path, and then three SHA256s, one RIPEMD160, and a Base58 conversion to turn that final public key in to an address.
Still, the account you are replying to is an AI spammer, which is why the script he shared is nonsense.