I agree with the former, but not the latter. Probably flatter than the typical "woofer plus tweeter with a massive canyon in the response where the woofer falls off and the tweeter hasn't kicked in yet" but flat in a bass cabinet from ANY manufacturer is not something I've ever found. You go on to mention studio monitors, which are also commonly not flat. Even monitors costing orders of magnitude more than any bass cab on the market aren't commonly flat in terms of response.Yes, they do have a very similar response curve, & that curve is flat!
Not that there's anything wrong with non-flat response curves.