Beluga was and is doing one-off charters to various airports, so loading/unloading is somehow solved, maybe not ideal but it works. Beluga cargo deck cross section is considerably larger than AN124/225 so it has a niche.
However as far as I've heard Begula is operating on some sort of dispensation given to Airbus as OEM because aircraft has only EASA Restricted Type Certificate, not full TC. I am wondering whether a "separate" commercial cargo airline can operate an aircraft with restricted TC?