I’ll counter that 90% of the time I’ve heard subwoofers they were not well integrated, so of course I’m not surprised that adding a subwoofer to a maggie by most sounds bad.
The issue IMHO is the TCO (total cost of ownership) of a sub is a lot higher than expected. Placement, measurement and EQ as well as acoustic treatments are often all needed to get to done. Most consumers want to drop the subwoofer in a convenient place and set the volume and call it a day.
I will say though, that subwoofers are often the last step on a list, not the first, that audiophiles should consider. Make sure your room is as well treated as you can stand. Often this tilts the balance towards the bass and makes a lot of speakers sound much larger. THEN if you still want a sub go get one. You’ll be in a much better place. Be prepared to get bass traps in the corners or soffits, and have a flexible EQ solution for the sub, whether built in or by using a miniDSP.
I can’t repeat enough that good room treatment will make most speakers sound much larger and more dynamic.