By what metric, exactly? Because I'd be willing to bet that it'll be smaller in terms of sales than FIFA 21 and this years COD game (those 2 probably beat it on PS4 by itself, let alone all versions combined). I kind of expect TLOU2 to outsell it as well.
When I said biggest I ment = budget, quality, graphics, expectations, wow-factor (you get CoD+Fifa every year) ect.
TLoU - part 2 + Final Fantasy 7 Remake + CyberPunk 2077 are the "big" tittles for 2020.
I think Ghost of Tsushima will be huge too... Ubisoft refused to do AC in Japan for over 10 years, people really want this game.