We should console ourselves with the knowledge that Juventus built a stadium that holds only about 41,000 and is widely considered the best in Italy. While I too believe 60k should have been our future-proof target, the main thing for us will be to build the best atmosphere possible. Having a capacity crowd every week will help us do that.
I think the Juventus comparison is a valid one for illustrative purposes. It is at the extreme end of the spectrum of approaches to building a new stadium. Pitching capacity particularly low, to minimise costs and really squeeze that supply/demand profile, to maximise ticket prices.
Of course, in their defence they had the opposite problem to us when they first embarked on their new stadium project. Attendances in Italian football had plummeted generally, and they had the cavernous and generally disliked 67k Delle Alpi, with its running track and whole tiers of empty seats most weeks. Plus their club had been involved in various damaging scandals too. So, in many ways their choice of capacity made sense, and seemed to have the desired effects. The fans responded positively. They filled it regularly and the atmosphere improved dramatically with the new tighter format. The gates started to drop off slightly after a few years, which they probably thought vindicated their capacity decision. Perhaps the novelty factor and new-stadium-effect had worn off slightly, or perhaps the club had pushed their ticket pricing a bit too far. However, there has since been an increase in attendances in Italy recently and the place is full every week again. Now Juve and some other Italian clubs are revising their stadium capacity ambitions. Roma had been looking at low 50s when they commissioned Meis originally. They're now looking towards mid 60s. The Milan clubs are doing similar, perhaps even 70k. Which brings us back to the future-proofing factor. Depending on the format chosen, sometimes when building a smaller stadium, optimising sightlines for that given lower capacity can make future expansion both more difficult and more expensive. As a result, Juventus are now even considering a whole new stadium.
I don't think that 53k is at that extreme low end of the scale for Everton. It is a sizeable increase (after all, 36k home seats up to 49k home seats is a 36% uplift). It may be close to that illusive "sweetspot," where they can still maximise income per seat (more than covering costs). The only issue there of course, being whether or not our fanbase can afford that financial squeeze. But, as with Juventus, it also poses the question about future expansion, if ever required. Not necessarily a pressing question just now..... but definitely a longer term consideration for any club.