Bol Zup your infomation is a little out.
To clear up a few things the controller on long term sick is no longer on it but is only validated on radar due to the need for radar controllers. As Heathrow Dictator says the problem is attrating and retaining staff on the lower wages. Incidently the figure he uses for MME is what the senior controllers are on, not the starting figure. As Heathrow Dictator says the radar unit can get very busy, as HD maybe finding out, where as the Tower can be very quiet. The underlying problem is there is a shortage of staff. This is almost entirely down to lack of funding of the ATC operation with low wages and a reluctance of the owners past and present to invest in equipment and better wages.