It's not about the recoil...at least not completely.Nothing wrong with straight blowback. I'd take a roller lock or radial delay over a blowback, sure, but not for 2x-3x the cost. It's a 9mm carbine, not a battle rifle. Recoil should not be an issue for most.
Although if someone has a line on a CMMG Banshee for a couple hundred bucks more than a PC Carbine or Beretta CX4, I've got a finder's fee for ya.
No, the recoil of a blowback gun is not at all unmanageable. But it's much higher than it needs to be due to the heavy bolt required to cope with the 9mm in a straight blowback system. All that mass travelling back and forth creates bounce and increases time between followup shots. A delayed or locked system allows for a much lighter bolt, and creates a much smoother and flatter recoiling system. Speed and fast target transitions is a huge part of the appeal in a 9mm PCC, so the extra cost is worth it in my mind.
If we're specifically talking about AR-style rifles, there are also other downsides to a straight blowback gun. The system was not designed for a solid bold like most blow back designed use, and employing one defeats the built-in out of battery protection designed into the AR platform. Straight blowback also relies on properly balanced springs and buffer weights that are tuned to the ammo, otherwise it can short-stroke and cause hammer-follow and doubling.
A system like the CMMG RDB design leverages a rotating bolt in a carrier just like the original AR design, it just eliminates the gas system. As such, it retains the out of battery protection from the original AR design and the lighter bolt and buffer provide a broader margin for error before the gun would short-stroke.
Yes, you can get a straight blowback gun that works, and you can get some that are tuned to run very well. But a locked or delayed system solves many of the inherent shortcomings of a blowback design, and is a mechanically superior solution IMO.
