I find this a very dubious argument for a couple of reasons:
1. Even in average seeing a 14" scope will perform better on deep sky and go significantly deeper than a 6" scope (note the design is irrelevant - frac or newt). Planets will also see some improvement.
2. Secondly, using this argument no one should buy even 6" refractors as the seeing will not support their full resolution. We should all use 100mm refractors and call it a day.
In my experience a larger aperture helps in all conditions. But that does not mean I recommend a large aperture scope to everyone. The ultimate choice is driven by personal preferences (convenience, observing style etc.). I am only trying to offer pros and cons of each here. Only the Op can decide what is right for him.
Merely stating my experience, not attempt to form an argument. Specific to the 6" apo and newt question asked, I have done it, and after a good amount of time that was the result I arrived at, for me.
I'd still have the TEC if I could afford it as I am also a fan of refractor views. Of course on globulars aperture always cleanly wins... but then if you want very wide a small refractor is pretty ideal, if not binoculars. To me there is no 'best' always. There is a lot out there that is at least very good IMO a lot of time if used within it's brackets.
A contrary POV would be that it took rare very good seeing for the newt to strut it's stuff for planetary while the 6" apo was always nice to view them with.
Throw money and not science or experience and location into the picture and it changes entirely for most folks, me included. For me we are in a modern golden age for amature astronomy. That someone could own both new for under $10k today, and get a mount for the refractor... is really to me impressive!
With the arrival of somewhat affordable large refractors for visual by that I mean ~150mm SW, TS, AT, APM, there are a lot of folks that can now at least try it for themselves for a fraction of the cost 10 yrs. ago. Goto Dob's a fraction of what it cost 10 years ago. Then there are all the other designs... imaging, video assisted, NV ... the times they are a changing!
I agree too that information on the web is not experience that can be somehow absorbed as it is the individuals experience that is the only yardstick. Did not mean to misrepresent anything.
So folks should buy stuff and get out and use it. then go to the eyepiece forum and ask about best eyepiece...