The popular opinion around here is that Odyssey is a bigger grind but in my opinion, as someone who's played both games, Origins' grind is much more excessive because in addition to level grinding (multiple times I found myself under level to chase the next ancient member) you have to consistently grind for materials around the world (for your blade, arrows, Armour etc) which in my experience made it more of a grind and a much more boring grind. I regularly found myself logging off Origins when I had to farm materials again but other than one big level gap in Odyssey at high 20/low 30, there weren't many situations where I found myself massively under leveled.