Element X is in some cases still a downgrade from Element. For instance there doesn't seem to be a way to create local key backups anymore. Also, that calls between Element and Element X are incompatible means both apps need to be installed in order to receive calls from all contacts.

Still, I love Matrix and hope that these issues will be resolved in time.

Manually importing/exporting keybackups is on the todo list (albeit towards the bottom). Supporting legacy calls is not (unless someone contributes it); the intention is to converge asap on native Matrix group calls.