Some of that is very true.. the WSSSM is falling from popularity in bolt action guns.
BUT- it is still up and coming in the AR because it fits in the the gun.

There has been more and more recent development with the WSSM line of cartridges in the AR. Most has been done by Mike Milli of Dedicated Technology in co-operation with Olympic Arms. Mike pioneered the WSSM in the AR.
He also loves the 25WSSM and hunts with it personally.

I have a 243WSSM.

The issue I have with the 25 cal version is that you are very limited on factory ammo. Most is too long to fit in the mag. If you handload it is not nearly an issue. I chose 243WSSM because all factory ammo fits and reloading there are many more choices for bullets available in 6mm than .25

Olympic last year released a 30 cal version that surpasses the 30-06 with heavy bullets. That's amazing when you consider that Remington's 30RAR can't even perform on par with the 308.

All of the WSSM cartridges outperform just about any other load in an AR in the same caliber. The 6.5/25WSSM puts the Grendel to shame. Heck even the 243WSSM outperforms the 6.5 Grendel.

I think there is a stigma with Olympic Arms and many won't consider a gun from them and dismiss anything that Olympic makes.

I did NOT buy my upper from Olympic. I went to the original designer. Mike Milli. It was only about $50 more coming from him with an accuracy guarantee.
www.dtechsuperstore.com
Give him a call, he'll point you the right way and won't be burnt if he can't make you what you want. He's a great guy, buy with confidence. BTW, wait times are about a year-plus. The reason I went with Mike instead of Oly was Oly's wait time was 8 months and Mike had me done in 2 months.

PM me if you have any other questions.
If you want to see examples/reviews of his rifles do a search on this predator hunting forum:
www.predatormastersforums.com
You'll be hard pressed if not impossible to find a bad review from hundreds of rifles sold there.