It was a snappy and evocative moniker, effective in what it was meant to convey. Ohtani didn't just pitch and hit -- he did both at elite levels. At the same time. We hadn't seen anything like it since Ruth, so the hype went.
The thing is, it has not turned out to be merely hype. Ohtani has not only lived up to the billing, he has left it behind -- like an old movie poster someone forgot to take down. Because comparing Ohtani to Ruth no longer makes sense: No one has excelled at pitching and hitting at the same time like Ohtani in the extant major leagues, not even Ruth. You can point to some of the great two-way Negro Leagues stars like Martin Dihigo, Bullet Rogan and Double Duty Radcliffe, but no one in the American League or National League.
Understand that this is not a claim that Ohtani is as good as Ruth, whose contributions to the game as a hitter are almost mythical. It's just to acknowledge that while Ruth was the only other AL or NL player who both hit and pitched at an All-Star level for an extended time in the same career, not even The Babe did so simultaneously.
Ruth split significant time between playing a position and pitching in only two seasons, 1918 and 1919. The closest Ruth came to what Ohtani has done was 1918, when he finished seventh in AL position player bWAR, 17th in pitching bWAR and fourth overall. Last season, 103 years later and in a much larger American League, Ohtani ranked 11th in position player bWAR, seventh in pitching bWAR and easily led the AL overall.
In other words, the Ruth comp was great for building anticipation for what Ohtani had to offer, but it no longer works. Ohtani is truly incomparable.
Or, is he? There is one player against whom it might still make sense to compare Ohtani: himself.