The problem being caused by third party add ons would make much more sense to me if I got repeated stutters in areas where I have third party add ons. Like I said though I get them well away from any scenery add ons. The middle of the mach loop being a good example. I get about a minute of huge stutters at the same point in the loop each time I fly it. Its so annoying.
Similarly elsewhere. Its in very specific locations and mostly well away from photogrammetry or third party scenery. Its definitely not caused by add ons, as far as I can see.