What you can do is try to make sure your polar alignment is tighter, that will help quite a bit here. I'm not sure how you're currently doing it, but you can start to build up "drift alignment" as a tool in your toolbox to supplement polar alignment.
https://www.cloudynights.com …ment-by-robert-vice-r2760
If you're precisely polar aligned, at wider FOV angles like you're using, you'll get tracking of 2~4+ minutes without much period error.
Other things as you already mentioned are ensuring your setup is balanced very precisely so that after it changes arcs the weight shift doesn't cause problems. Also, less strain on the worm gear and cogs if you're balanced properly. Weight matters a lot, and when you're at the limits of the mount or undermounted, this kind of issue is prevelant. If you overmount, you'll have it a lot easier. You can look to shed some weight by considering that you don't need to use that 70-200 and instead, get a simple prime lens in the focal length that you prefer for FOV. You don't have to use an AF Canon lens. You can instead use inexpensive high quality primes that are legacy, such as M42 (Pentax) mount Super Takumar lenses adapted to the EF mount. You could a 50mm F1.4, 135mm F3.5, 200mm F4, etc, all lighter weight, inxepensive, sharp, good multi-coating, and you can stop them down 1~2 stops to get really good coma control and sharpness for cheap and help manage any CA. Worth toying with for these purposes. The 135mm and 200mm are excellent for wide field groupings like you're doing here.
Very best,