In my mind, while there were similarities, there were 3 broad categories:
Tier 1: Mens health & the lie, for guys who take jogging and bosu ball curls as seriously as squats and deadlifts. Front cover callouts that wouldnt look out of place on a woman’s mag i.e. 6 weeks to a slimmer waist for summer.
Tier 2: Muscle & Fitness, a halfway house between MH and tier 3, for the gym bro’s who like to lift but still wanna claim natty, aspires to do physique and contains generic split of some physique competitor (spoiler: same split as the BB Pro)
Tier 3: Flex, just as you said. Huge dude’s post olympia pics on the front, big arm blast routine callout, half the pages are full of supplement ads (more so than tier 1 or 2), My Olympias secret uncovered split (still a 5 day split, but instead of 5 x 10, he does 11 reps on the first and last set)