Seeing does not "limit" SCTs any more than other scopes.
I assume you meant for identical aperture scopes.
However, that has not been the case, in my experience. The AP Mak Cass seems to deal with seeing better than 11" SCTs. That is most likely due to how the AP handles the thermal equilibration issue, and thus the atmospheric turbulence adjacent to the primary and the baffle tube (i.e., highly local seeing).
IIRC, Roland Christen had suggested that OTAs with better optics can handle seeing better than those with lesser quality optics. Unfortunately, I don't recall the points of his argument.
No, primaries on Dobs don't usually dew over. If they do, it is because they are picking it up from the ground
. Maybe my remark was misleading because I used the word "dew," so sorry about that. If the ground is wet, like pretty much any time before August, the primary will get wet too. The mirror box is open on the bottom and very close to the turf.
My 8" f/6 Discovery (Terry O. mirror) is a nice scope and once cooled it delivers more detail than my 5" f/12 refractor. (As I noted in my OP, the thing is gigantic for its aperture and somewhat redundant since I have a TV101 now.) My only real complaint is that its aperture limits its ability to find details on Mars or the possibility of details on Uranus. I have a dew chaser on my secondary and am resigned to getting one for a CAT if I go that direction. The solid tube 8" doesn't need one.
I know that all else being equal a good newt will outperform a similar size SCT and that a good refractor of that size will outperform any of them. The thing is usability. I can put a fork mounted SCT on wheeled thing in the garage and roll it out ready to go. I can't do that for an EQ-platform truss dob. It would be too shaky and the position of the base of the EQ platform is too critical. Plus, as I said, mine stopped working. And there's the need to sit on the ground to view Sagittarius and the inability to see over the neighbor's hedges if the planet is low in the sky, which it often is.
I know I did not mention this before, but I am also looking down the line to the day I can build a back yard observatory, and the short, tripod mounted SCT is just more observatory friendly than a Dob.