MAN is probably just as well, or even better off than DUB, considering DUB DOES have a based scheduled airline.
The 2 routes DUB does have that MAN could use are BOS and YYZ on AC.
We have a US A333 to PHL (meaning US have more capacity ex-MAN than LHR), 2 daily CO, AA to JFK/ORD, DL to ATL/ATL, VS to MCO, BGI and LAS, EK to DXB with the A380, QR to DOH, EY to AUH, PK to ISB/LHE/JFK/KHI, SQ to SIN and so on long haul.
Also, LH has flights to BRU via SN/FRA/MUC/STR/CGN via 4U/HAM. Anyway, you get the picture.
Yes, MAN can do better, and MIA looks to be added by AA next winter, HKG is a route that could easily be filled and some euro gaps could be filled. But lets not take pity on MAN, for we have a very very enviable route structure.