You have to keep this in context. We are talking a $600 6" Refractor. You cannot compare it to a $7000 Esprit 6". It's like comparing a corolla to a mercedes. Have you tried double stacking with a Baader semi apo?
Newtonians are very affordable but the diffraction spikes in images are annoying to me. Just a personal preference, some people like them. I like astro images to be more accurate representations, not flooded with unnecessary optical artifacts.
I had the pleasure of spending 3 nights recently with my mates Skywatcher 190mm Maksutov-Newtonian - now THAT'S a telescope! Massively overlooked by people. Perfect pinpoint stars across the entire field, simply AMAZING views. No diffraction spikes, beautiful pinpoint stars. No coma or field curvature. Very sharp. Wide field but fully corrected, Apo performance for a fraction of the price.
I'm going to be getting one of these SW Mak-Newt's on a Celestron CGX mount which I prefer. I like the planewave software with the CGX, and when i spent time with the cgx in the field, it and me just 'clicked'
I would recommend anyone looking for large aperture APO performance at only the 2K mark to go and experience the SW Maksutov-Newtonian.
Cheers,
Mark