I guess you have to reconcile the two. You can't really satisfy both problems. Adding a citizenship question may seem like a way to do both, but as it could effectively be used to locate illegal immigrants they would be less likely to fill it out, which would then defeat the purpose of the compromise.
I am someone that tends to think the "founders are always right" approach is a poor one, but I haven't seen a proposal that takes my position and your position into account successfully.
There are estimations of the population of the citizenry, which could be used instead of the census for apportionment of representatives, but I prefer the hard number to the soft one. Soft numbers decrease confidence in the system. Hmmm. I don't know tbh.