Nope. JP has been making RLGS 18" Grendels for almost as long as 6.5 Grendel rifles have been in production-one of the early adopters, and those guns run great.
18" MLGS Grendel runs great with .076" ports. .082" is a bit large for my liking, but not as bad as .094" ports on MLGS. If you see .094" MLGS 18", you will really need to choke it on the front, and tame it in the back as well.
I have had 5 different Grendels. The longer the gas system, the smoother the rifle shoots, and the easier it is to mitigate the already low recoil of the Grendel. Shorter gas systems usually create more recoil, faster operating speeds for the bolt/bolt carrier. I have found that I prefer the rifle length gas systems.
You can change the weight of the buffer regardless of whether you have a rifle, or carbine buffer system. You can also use an adjustable gas system. The smoothest system I have had was a rifle length gas tube, adjustable gas block, with a rifle buffer system that I added one extra heavy weight into. That was one smooth shooting rifle.
Something else I found out is that with shorter gas systems, the primers tend to show a little more flattening. Rounds that looked fine in my rifle length gas system gun, showed a little more primer flattening in the gun with the shorter gas system.
TonyTheTiger is right about brass abuse..I had forgotten about the primer issue until Tony mentioned brass abuse. I never worried much about it as the Chronograph confirmed what I had hoped by not loading max powder charges...that I was well within normal velocities. I used Lapua brass and quit counting how many loadings I got from the brass after about 8-10 loadings. Once I hit 8-10 loadings I would get about 2-4 case failures per 100 rounds even though cases were annealed. Failures were loose primer pockets and a few cracked necks even though the cases got regular annealing.