How do I get the private key to an address?
This is one of the most noticeable differences. With descriptor wallets, you cannot export the private key for one address. This is because a child private key combined with the parent public key can be used to compute the parent private key (and hence all other child private keys). This is a risk inherent in BIP 32's unhardened derivation. As such, descriptor wallets disallow the export of child private keys in order to mitigate the risk of accidentally exposing the parent private key.
Wouldn't it have been a much better choice to use hardened derivation?
But you shouldn't be exporting individual private keys anyways. The wallet does not use just one private key, so having an individual child private key is really not that useful.
I can think of something: I needed to use CPFP, but Bitcoin Core's GUI didn't allow me to use an unconfirmed input from a third party, so I exported the private key and imported it into Electrum.
I guess I'll have to give up my non-HD-wallet eventually, but I don't like it. Importing a private key is so much easier without descriptor wallets.