You’d also be violating the CONST_SCRIPTCODE standardness check, I think, because you’d need FindAndDelete to actually delete the signature from the scriptcode (or you’d need to use OP_CODESEP to do the same thing manually). Would probably also mean you need two CHECKSIG ops, one in the scriptSig for CTV, and one in the scriptPubKey so that it’s not anyone can spend. You’d also presumably need to repeat the public key, though could possibly at least reuse the signature.
Not doing it as p2sh would also make it cumbersome to have any more complicated logic in your spending condition.