Could they fill something "significantly larger", though, at the frequency they offer?
Loganair fly Southampton-Edinburgh 3x daily with a 49-seat aircraft.
EasyJet fly Southampton-Glasgow 1x daily with a 156 (A319) or 186 (A320) seat aircraft. And, as we've seen, similar prices.
It's the same here. Loganair fly 4x daily to Manchester/Liverpool with a 72-seat aircraft. EasyJet will fly 1x daily during midweek and 2x daily on Fridays and Sundays with a 156-seat (A319) aircraft.
Drip pricing pays off for people who are able to travel with a small rucksack. For everyone else, there's bugger all difference in price, especially now the 'large cabin bag' option on EasyJet is usually only £1-£2 cheaper than the 15kg hold bag option. And judging by the number of people I see who get caught out by just how small the 'small cabin bag' really is, I'd say most people need to take more than the 'small cabin bag'.
But, as always, YMMV.
I fully endorse them not taxing the first four litres and 200 sticks of finest aviation spirit