Is this about the gui not offering e.g. the wrong algorithm or key sizes in the first place? If so, then we have to either hard-code it in kleopatra, or communicate it from gnupg. I guess at this point, we'll have to hard-code it :/
Fwiw, gnupg kind of refuses to create non-conforming keys, but this is rather by accident. It creates the key, and then fails to create the self-signature because the key is not compliant. Only interactive keygeneration actually take the compliance mode into consideration.
Actually, Andre has some uncommitted changes that do implement the wanted behavior. AIUI those mainly needs a little fix to so that it wont break with old GPGME versions. Once merged, I will amend it further if necessary.