Just not even really comparable players, didn't even play the same position. Allen is up there as one of the greatest pure shooters of all-time. Johnson was a much better defender. Allen wasn't a bad defender by any means, but Johnson was an historically good defensive player. I'll take a plus defender over a plus shooter, though.
I think Garnett, over the course of his career, was probably better than Bird (I'm not a Celtics fan, so I don't have a dog in this fight). I'd struggle to name 10 basketball players better than KG (Jordan, LeBron, Shaq, Russell, Magic, Kobe, Wilt, Kareem, Duncan... and that's it). He might be the best defensive player of the modern era. And of those guys, he's the only one who spent the majority of his career on remarkably ****ty teams rather than surrounded by other Hall of Famers. Call him the most underrated player in NBA history and it wouldn't be undeserved.