Hot take: I always thought rounding the spine was just for looks until I saw one hold up 40 years
A retired binder in Portland showed me a 1984 ledger he did with a rounded and backed spine, and that book still opened flat without cracking after four decades of daily use. I had been squaring off every spine for years because it felt sturdier, but the shape of that rounding is what takes the strain off the hinge. Does anyone here still round and back by hand, and if so, what do you use to keep the shoulder even?