There is a difference between a concept being an allegory, and the execution of the concept being all about
the allegory. Singer in 1, 2 and most of 3 spent far too much time on the philosophising, and nowhere near enough time on the "POW! BAM! ZAP!"
The X-Men and Magneto in the first two and a half films are pathetically weak, and have few chances on screen to demonstrate their true power. The only time Magneto in particular was written properly powers wise was the lifting of the Golden Gate Bridge. He NEVER got Jean/Phoenix right except the little "teaser" bit at the end of 2.
In short, however good some things might have been about the first 3 films, they failed to "embrace the spandex" and thus fail as superhero
movies, which makes the approach in FC the far superior version, and Singer had the least to do with that film.