The bloaty key/signature size is only a problem with the PQ encryption systems.

For signing only there are much more efficient PQ cryptosystems, with signatures around the same size as ECC. If DNSSEC ever adopts PQC it will be one of those systems.

Here are two of the earliest, and easiest to understand. There are much better ones now.

https://en.wikipedia.org/wiki/Lamport_signature#Short_keys_a...

https://en.wikipedia.org/wiki/Merkle_signature_scheme