I wouldn't call it far superior. Griezmann scored 10 more, assisted less, but also player for far weaker teams. As good as Atletico is, they were a good step behind Real last year and usually score much less goals than Real. And one season he played for an average Sociedad side, where he scored 16 in the league as a winger, that's pretty respectable too. We can only imagine how it would look if Griezmann played 2 seasons for Real and Bale for Atletico and Sociedad. I think there would be a good chance that Bale couldn't compete at all. For me, Griezmann was better the last 2 years anyway, stats are not everything, Bales last season is a good proof for that.
He is also younger of course, for me that's just a signing Real/Barca usually do, Griezmann, De Bruyne, Verratti, Pogba, the next potentially superstars, who want to win everything. Better for me than they guys who did it already at Real/Barca 4 years later and will only join us because of money and because their "dream club" want to get rid like Bale or that Angel guy.