When generating a .psbt it suffices to merely import the address (hashed Public Key) in Electrum while in BitcoinCore (for the same address) I also would have to import either a corresponding Public Key or Descriptor. Is there a reason why BitcoinCore requires these additional inputs and Electrum does not?
Bitcoin Core requires the additional data so that it can estimate the size of the final transaction when it is choosing which inputs to spend. It is probable that Electrum makes assumptions about the size because it is standard, however Bitcoin Core does not do that. Instead it will make a fake scriptSig/witness to determine the size of the input, and doing that requires knowing public keys and other information provided in descriptors.