What is wrong with a sub?

Subs fill in the 'bottom' that the majority of speakers can't 'reach', w/out distorting their 'upper' frequencies.  Case in point:
 
I happened to be @ a instrument b&m store where some musicians started goofing about with various 'toys'.  While the 'regular frequencies' (80hz+) were covered by the monitors Just Fine, the 'subs' (which had 'ribbons' @ their ports, wagging about...) were 'filling in' the bassline that the monitors 'faded' from.  So, I took that as an 'instructive moment' that Any speaker shouldn't be expected to cover Everything....esp. when it came to moving 'bass line air'....since bass is mostly 'air movement' @ a major (and physical) process.  The aforementioned 'ribbons' were wagging about, in and out of their ports.  It's just how much 'air' you can excite, pure physics....

You want 'concert sound'?  Subs.

I'm too new and inexperienced to take a side.  But as I posted - I like tube amps.  I like how they sound.  As such at reasonable price range tube amps there are no ribbon speakers I can use.  The subs having their own amps move the air fine.  I also like the argument that the position of the subs may not be where the mids are.  

Good subs add an "atmospheric" thing to a hifi system that has to do with charging the room with frequencies that exist in real music played live, not necessarily chest thumping low notes although they can do that also of course. My my main speakers have a very accurate low frequency range that sounds excellent without subs, but dial in the subs and man...something is just there that ain't otherwise...orchestral music sounds like it's in a real acoustic space, pianos sound like hey, that sounds like a piano! Subs aren't and never have been "lacking respect" in the audio community so don't get hung up on low notes, simply enjoy something closer to what music is supposed to sound like.

first 2 subs are a lot better. I have 2 and have experimented running just one. No comparison  The Achilles Heel  is when come with a built in plate amp with volume control and cross over point. Most of these are crude and cheap

Emerald Physics make a interfacing product called The BOM (bass management) which works pretty well for ~ $300, but to get the best Marchand offers excellent outboard active XOs, but they are costly