Just a few thoughts on this:
1/ Due to the nature of its operation (pilgrimage charters to Lourdes, VIP/corporate charters), Air Mediterranee is an infrequent visitor to airports in the UK. That might explain some of the confusion in STN (if not in MAN)
2/ In that case, the safe thing to do for the dispatcher is to review/confirm the loading instruction with the flight crew
3/ There might be some issues in case of split loading (e.g. some airlines want destination baggage in one hold, transfer baggage in another; if much less [or more] of one category turns up than expected, the loading instruction [sometimes prepared hours before] might end up wrong)
4/ Long, thin aircraft are more loading- and trim-sensitive; e.g. A321 vs A319, B738/739 vs 733, etc.
Never been a big fan of centralised load control; loading issues are more easily (and quickly) dealt with at the gate or on station than by someone in an office 300 miles away (or more) - provided of course the local dispatcher is properly qualified and conversant with loading and M&B issues.
Regarding Ryanair, standard loading on 738s is first 160 bags in H2, then load H1, then rear holds (H3, H4). With FR charging for hold luggage, H1 is rarely loaded let alone full. PAX-wise, the Cabin Crew will indeed automatically block a number of rows depending on PAX figures. Since PAX board Ryanair flights using both front & rear steps, they usually spread out quite evenly in the cabin while choosing their seats.