Not to argue semantics, but no, that’s actually not what it means. It means they’re not a good value if buying only or primarily for gaming, a point I made. It doesn’t mean they “aren’t good for them.”
OP also asked if getting a new garbage can Mac would help. It would, but it would be an awfully expensive option for the computing power. The iMac, however, seems to be benchmarking pretty solidly. I didn’t expect that, given the number of pixels it has to push, but there it is.
I agree with you as a very general statement, at least if you’re someone who’s use to Macs. I use both platforms and I feel I’m far more effective in Mac OS. But, if you’re buying a machine primarily for game development with UE4, Darth is absolutely right. It’s the same equation as buying a gaming rig. You’ll get a lot more for your money if you go Windows (or Linux, but really…), and most of the consumer-targeted Macs that Apple makes do have less than stellar graphics cards.