What do you mean? Any WIF key can easily be converted to an address by many different libraries in many languages that could easily confirm Bitcoin Core is not "outputting gibberish".
Yes, you can take additional steps to convert the WIF key into an address and use that to confirm that it is indeed the correct key. However, from observing other threads and guides that discuss using
dumpprivkey to show that the wallet has the private key, most do not go beyond just using
dumpprivkey and getting a string output. The point was that if you're trusting the wallet to output a private key that purports to be for a particular address (and aren't doing any further verification of that), then you can just as well trust it when it says it has the private key for an address.
No, a real user is telling you it's actually more difficult. You'd likely benefit by taking their input into consideration. A bunch of core devs probably isn't the best test group for usability. Just because someone knows more about something than someone else, doesn't mean they know best.
And real users have demonstrated confusion and difficulty with using just private keys and moving them to different wallets. The only input I'm seeing here is "this is new and I don't know how to use it".
I have seen people complaining about not being able to see their address(es) because they imported their key(s) into a wallet that only makes a specific type of address. I have seen people confused why when they import a xpub or xprv that the wallet generates a completely different set of addresses than they are expecting. Descriptor solve these problems by explicitly stating what kind of addresses to create and what the derivation paths are.