Just for the record the reason for the decrease in SEN numbers for May year on year is down to it being a 3-aircraft rather than 4-aircraft easyJet base this year. It wouldn't be true to say that this suggests SEN "has reached its popularity threshold". A simple illustration of that is that SEN-AMS has varied between 3 x daily and 2 x daily in recent times and each time that it is increased pax numbers rise in line with the capacity increase.
I don't have any doubt that if easyJet revert to 4 aircraft next year that additional capacity will be easily filled.
Personally I'm really pleased to see LTN's continued passenger growth as that means the industry is growing strongly and if SEN's marketing department do their job there's no reason why they likewise shouldn't benefit from that growth. There is, of course, no comparison whatever between the prospects for LTN and SEN and the latter will always be an 'also ran' as far as the LON market is concerned but 2 mppa plus shouldn't be unachievable.