But the plus argument also is that clearly, despite overall seat capacity at both airports, Jet2 are able to fill more seats out of MAN than LBA. If there's less routes and based A/C but more seats available - that's the big factor to look at. If you looked at routes vs A/C - MAN would be on a winner hands-down.
Clearly LBA can only be managing the ~148 seats on a flight when MAN can be achieving ~180 and even up to ~220 filled seats per flight more often. Number of routes and based A/C doesn't mean all that much, honestly, MAN is a more competitive field than LBA is which would be a good reason for less routes meaning less based A/C.