well that it’s required is true but I think it’s just inefficient.
for mis-signings they could just drop the old mis-signed response and sign a new proper one. I didnt even say that the client needs to cache it for all eternity, but it would already help to remove a lot of overhead if an old revocation signature would be accepted in browsers, while this still doesnt remove the “problem” of having to store the signature, it at least eases the computation usage.
going back to the 90 day lifetimes
that neglected certs pass away faster is certainly true but then again short certs have also quite a signing overhead from active domains because you have a 30 day overlap at the beginning and end of each certificate meaning that any certificate in the “middle” has only 30 days to stay alone, meaning that half of the year, 2 certs have to be signed with OCSP (giving a 50% increase on the OCSP for active certs). also you have to sign 6 certs per year instead of just 1 (well due to a few days overlap depending on an admin but it probably wont exceed an average of 1.08 certs per year, coming to the same 1 month overlap) with a 1 month overlap you have to double-sign only 2/12 if the lifetime (1 month at the beginning and end each) giving 1/´6 or about 17% overhead on the OCSP.
of course that overhead could be greatly reduced if the revocation would remove the need of new OCSP responses by just revoking the old certs but you would still have to keep the signatures for all the time.
so assuming that most certs are used actively, actually longer certs have less overhead.