Could have guessed, T3 is the worst terminal at MAN. Security is poor and the small corridor after security is chaotic if there is a flight boarding on a nearby gate.
Station quite a way (10 minute walk) from the check in however this is similar at Heathrow. The only difference at Heathrow is that you don't leave the building on the way to check in. I suspect that this is why it feels longer to get to check in at MAN. There are at least three lifts and two buildings between the station and T3.