Yes, the long bullets won’t be seated optimally. The short mags really come into their own when they can be seated out in a medium or long action. I’ve realized this myself with a 7 SAUM.
That being said, I am putting together a multi-barrel short action hunter for 223, 6.5, and 300 WSM. While I know the 300 wsm will be a bit held back, I’d love to see how much ground can be made back up with R26?? If you can get it over 2800 in a 22-24” barrel, then I think it will really perform.