I just had Michelin Defender M/S 2 285/65/R18 116T (XL rating) tires installed on my stock 200, and oh boy is this a treat. The 200 rides like a Cadillac now, and that’s coming from somebody who had Michelin Defender M/S in 275/65/R18 previously on.
Not sure what magic Michelin did, but these new tires absorb most of the small undulations in the road, and they are perfectly balanced with no weird vibrations at high speeds.
I would definitely recommend the 285/65/R18 tire size, but make sure to get the 116T rating for a much more plush ride (assuming you’re not doing a ton of off-roading of course, as there are better options than the defenders for that).
Do you know what load index your previous 275/65R18s were?
Besides the noted difference M/S and M/S2s.
As a size, 275/65R18s have continued to prove as a poor riding tire due to the increased pressure requirements and square sidewall geometry reducing compliance. I find it strange why so many still gravitate to fitting 275s...
Granted size options in 18s are minimal but to your point 285 and even 295s are better options IMO.