Along this line, wasn't there still a fair amount of debate about the size and shape of the earth? Many still held the notion the earth was essentially flat?
Nobody who mattered. Anyone in Europe with even a modest education knew the world was round.
Those who did understand that the earth was basically spherical, might argue the dimensions, and thereby the length of voyages. Eratosthenes & Ptolemy made mathematical calculations of the earth's circumference that had a fairly wide variance and both theories were known in some circles (small pun intended..) before and during the age of exploration.
Nearly everyone who was educated accepted Eratosthenes' (fairly accurate) calculation of the Earth's diameter. Columbus cited Ptolemy's estimate, largely because if Eratosthenes was right, his voyage had no chance of success.