Take it for what it's worth, as I think vests are like boots, meaning they can be unique to the individual. I've used a RNG-200 as my primary vest (I primarily alternate between it, a Dixon, or no vest at all based on where I'm hunting and time of season) for the past four seasons. I've found the seat to be overall comfortable, but not necessarily something I'd want to sit on for more than a couple of hours. But for me, I'm rarely ever going to sit that long. It does seem like it is less comfortable than when it was new.
I bought the Sitka vest recently for its somewhat similar minimalist style, but with a larger pack to better-accommodate a bladder plus more storage for shedding layers on long-all day hunts where I may be covering a lot of miles. I was curious how the thin seat would work out, and time will tell as I put some miles on it, but I used it this morning on a hunt for the first time and so far so good.
My buddy and I set up on a bird, and from the time we set up to when he finally pulled the trigger was exactly two hours and not once did I feel even the slightest bit uncomfortable. I was actually pretty shocked as I didn't realize we'd been set up that long. Obviously, it's a sample of one and I plan to run it through the motions this season, but my initial reaction was that it actually seemed more comfortable than the RNG.
And I'm about as far from a Sitka fanboy as you can get
I bought it purely based on the design and what it offered for how I like to hunt. Hope this helps.