Agreed and kudos to doing it right. It's not a "hook it up and just run with it" kind of thing, but takes the right tools to do sufficient measuring and setup tweaking to get a sub to integrate properly enough to really be useful in making trustworthy for mix decisions, IME. Not everyone is going to be up for doing all that. Can be easier and is likely to be less problematic for many to use slightly larger monitors that go low enough, and then just ignore the bottom couple octaves. Sure, that kind of setup which is not using a subwoofer will also benefit from a carefully made measured correction, but doing that will be significantly simpler than also implementing a sufficiently transparent cross over from the speakers to a sub.
tl;dr- smaller monitors + sub can be more complicated to get right than slightly larger monitors that go sufficiently deep.. as long as they don't attempt to go super deep or super loud.
That said, sitting close in a near field arrangement is the #1 thing one can do and costs nothing.