I dont know, KLM seems to be good at capturing pax in the smaller airports, and closeness to HUY shouldnt matter.
It operates MME/NCL, both close to each other, LPL/MAN both close to each other and im sure they do BRS/CWL that are close to each other.
Im sure there is scope for maybe a 3 daily F70 operation at least, as sheffield/Doncaster are large enough to support the market, and dont forget its not just AMS they offer, its the multitude of connections thereafter