Was Ohtani's game great? Absolutely. But it's being massively overrated because he pitched and hit in the same game. Sure, that in itself is great. But three home runs is not even close to being the greatest offensive feat ever done. 10 ks? Good game. But that is done with regularity any more. Yeah, they were done in the same game. Awesome. Great game. But greatest ever? Nope. I'd consider a perfect game better. Even without a single at bat taken.
4 home runs hit in a single game has been done 21 times. Those were better. Rookie Nick Kurtz just this year went 6-6 with 4 HRs, narrowly missing a 5th by inches. 19 total bases. 8 RBIs. 6 runs scored. That was a better game than Ohtani's.
Ohtani's game is overrated because he pitched and hit in the same game, going 6 innings. Babe Ruth pitched a complete game shutout, went 3-5 with a HR. Yep. Only 1 HR. But just as good if not better because of the pitching side of it. Just because nobody has done it for years before Ohtani came along, doesn't mean it's never been done.
A very good pitching outing that would be forgotten about by the next day by itself. A very good offensive game by itself that would be talked about for a week or so, then forgotten. The two of them together is what makes it an all timer game, no doubt. But greatest ever? Nope.