Sometime back even i used to think that 5th gen will be the norm of the future.But i think i was wrong.5Th gen aircrafts act as force multiplier in case of a full blown war or even low level kinetic strikes(like Operation Eldorado canyon or last years balakot strike).They can conduct SEAD/DEAD missions and other A2A roles really well,and BVR will be their niche.
But they have some really big shortcomings.To minimise the RCS they often have to compromise the on aerodynamics and have to carry weapons concealed in the IWB.They are really maintenance intensive,their RAM paints needs to be redone everytime after every sortie.And because these jets have to carry weapons inside their IWB they have to compromise on payload and that can be a real bummer in A2G roles.These are major design limitations.
Just look at Loadout configuration of Dassault rafale and the F-35.
Rafale can carry bombs on triple ejector racks on 2 pylons with 6 bombs in total with still 3 fuel tanks+4 BVR AAM+2 WVRCCM.
And even despite F-35 being available americans are still purchasing more Hornets more Eagles and trying to keep the F-16 in service.Rafale will easily live post 2060.
With Right EW and VLO design and other sensors 4th gen jets will live for really long.