small but crucial differences
Matching the engine and pylon to the airframe is an engineering art too. Four55000lb slst engines might promise 0.56lb fuel burn per lb thrust per hour. Two more modern 110000lb slst engines might promise 0.55lb instead of 0.56lb which is a 2% improvement.
Not only that but despite being physically larger it may be possible to integrate the two more cleanly than the four into the airframe and sneak economic cruise up by 0.01M from 0.83 to 0.84 or 0.84 to 0.85 or something like it.
There does of course come a point when a large engine becomes so large as to impose so much drag that there is no point in having it.
As far as maintenance goes it is to be hoped that the amount of time spent up ladders and poking things is about the same regardless of size. Or at least roughly the same. Maintenance costs are then lower because the time spent peering down holes with poles is halved. Engineers can tell you if this is spurious or not because some engines are more fiddly than others. But bean counters just see engineers up ladders hinging up covers and then folding 'em back down again. Fewer engines less cost, Carruthers old chap.
It would be a strange world if things were equal.... cats v dogs, blue v red, GE v RR, Company "A" v Company "B", twin v quad. I think it's the work of the devil sowing discontent in the amiable fraternity/sorority where never a fractious opinion is offered.
Who's for a whopping single then? Or better still, none at all but gravity waves wafted up from generating stations?