We argue all the time over this and unfortunately we have no science other than our gut instinct to back it up. We've read plenty of studies and usually can shoot them down because of 'real world' practice being very different to the methodology of the study. We've studies showing full conversion in 20 minutes. We've an argument that full conversion is not the same as complete de-branching. We've an argument that enzymes work orders of magnitude slower at lower temperatures, but that a mixture of enzymes are present with various levels of denaturing and natural variation alongside various grist compositions.
Define your goals. Pick a sensible starting point and stick to it. If you are not getting the desired results adjust one variable at a time. We stick to 60 minutes because it is a standard and why break it if it isn't broken? We might have to break it sometime, but they'll be easier things to change before that day.
Unfortunately it is very easy (forgiving) to make normal beer, there is a wide margin where things work out. Things only need to get more complicated when you start to step outside of the rules that define normal and touch on extremes. As an example it is very easy to get a beer to finish at 6-7 when it starts at 37. If you want that beer to finish at 16 you are going to have to do something complicated. It is very easy to get a beer to finish at 16 when it starts at 80, if you want it to finish at 6-7 you are going to have to do something complicated (or simple, depending on where you draw lines).
So what do I believe? Altering mash temperatures in the range of a degree or two will help a bit, but unfortunately not as much as we might hope. The difference between a final gravity of 8 and one of 10 is most likely undetectable and more a matter for cost and efficiency. The primary decider for final gravity is grist composition and yeast. We give things a helping hand, like a big beer might get a little longer in the mash tun if we've time and a slightly lower temperature mash if we remember (it is easier with big beers because the liquor to grist ratio often gets low due to capacity and thus you can miss a strike temperature) and a slightly higher temperature towards the end of fermentation and maybe a co2 rouse in the hope of getting it a little drier if this is desired, but this is not because the difference between 9 and 11 is detectable by the drinker this is generally because we need to hit a target abv and we are unable to fit any more grain into the mash tun and we want to use as little dextrose as possible. Dark beers always finish high due to the make up of the grist and are usually a compromise between mashing as high as we dare.
Equally an average beer might get a helping hand to make it a little more attractive to those who are particularly price conscious, but generally weaker beers need enough malt and don't want to finish too dry unless that is the intent.
Talking of british breweries these are the companies that developed modern macro brewing and are currently dying off due to decades of pushing watered down products driven by cost, efficiency and process upon increasingly reluctant consumers. They'll brew at high gravity and liquor back (dilute) to produce more beer or a range of beers using less plant. They'll grind almost to flour using wet rollers to get the highest efficiency and they'll mash as low as possible for as long as possible and sparge to death with a mash filter to wring every penny from the grain. They'll use hop extracts and oils to prevent losses to absorption. They'll centrifuge and filter then compress and reclaim the moisture from the yeast to blend it back into the beer to prevent losses to the yeast cake. Honestly, some of these practices are admirable and enviable and have allowed beer to be produced at a price to suit, but not all of them are for the benefit of the beer or should be sought to be reproduced. I would say that a 90 minute mash is an efficiency thing.