All seats get there at the same time, the only bug bear is for the recovery teams when the plane crashes and burns everyone beyond recognition. then the seated order on the manifest kicks in.
My family booked with Jet2 and had similar problems.  Also the hand baggage allowance went down in weight to 8 KG, (most bags weigh 1-2 KG empty) and the checked luggage weight went down too.
Everyone is at it these days of give as little as possible take as much as possible.