I haven't done any of the Firm tapes, but have read comparisons of Supersets, Push/Pull, and Bootcamp to the Firm. I think these comparisons were due to the fast pace and frequent equipment changes in those workouts, not necessarily the intensity of them. In fact, I think even Legs and Glutes was compared to the Firm, as it uses lighter weights and goes at a faster pace... Thinking about it, some of these might also have been compared to Fitprime, in that Cathes uses some unusual and new moves...
Wendy