BTW the Legion sold very well during the 60s so much so as they wentr froma backup feature in Adventure (to Superboy's lead) to taking over the mag. As well as Superboy's mag too later.
Actually I think they sold well up until near the end of the run of the two books which ran concurrent, Legion of Super Heroes and Legionnaires. The Giffen "adult Legion" strip didn't sell well, and that was the beginning of the Legion's recent sales woes. After Legionnaires and LSH was dropped, we went through Legion Lost, Legion World and The Legion, all of which didn't do too well I think. This is why DC did their current reboot.
I think the reboot had good intentions, which was to restore some of the things DC felt the fans liked about the Legion, which was the code names and basic structure of the Legion, but they ended up adding new factors like the youth vs. adult conflict. I also note they now have a limit on the number of Legionnaires who can be active Super Heroes due to the flight rings. Way back in the original strip they had a limit of 25 members according to a silly UP law.