I too have an MP200 (along with several other cartridges all premounted on headshells) and experience absolutely no inner groove distortion. Something must be off on your alignment or adjustments.
looking for advice to mitigate inner groove distortion
I currently have a Nagaoka MP200 on a rega P3 with all the groovetracer upgrades (including counterweight for better tracking). I've calibrated the cart using the Stevenson method but I am plagued by inner groove distortion. I'm considering getting a MP500 with the line contact diamond to help. Is this a good idea? I know IGD is part of the deal with Vinyl but I get bummed out every time the last song on the record comes on.