I think the comparison between Fuji's and Pentax's big zooms came up before in another thread. The same video was referenced if I'm not mistaken.
I have both lenses. The Fuji lens is a bit chintzy compared to the Pentax lens. You could probably beat an ogre to death with the Pentax lens and not lose alignment of the optical elements inside. Yes, Fuji's teeny foot is a miss compared to the rock solid unit on the Pentax lens. I feel like the Pentax lens is sharper for the same field of view and depth of field, especially with the K-1's 36 MP sensor.
However, I don't think the Fuji lens is as bad as some would want you to think. Optically, it's a good lens but not a great lens.
One thing the Fuji lens has going for it is the AF-C capabilities when coupled with a body like the X-T3. I photograph my kid's soccer games in low speed continuous mode and my low speed setting is configured to 5 FPS. I stand behind the goal, off to one side. When my boys have the ball and approach the goals I hold down the shutter button. The shutter starts cycling and damn near every shot from midfield to the goal is in focus. Imagine a burst of 20 to 50 frames and 90+% of them are in focus! And, I'm zooming out as my boys are running toward the goal. 5% of the frames are missed because I didn't track my boys well enough, 2.5% of the frames are lost because someone was in front of my boys, and 2.5% of the frames are just the camera missing what would/should have been a good shot. So, as a system, the lens works pretty good! There is no way the K-1 with 150-450mm can come close to that ... and maybe Ricoh never really wanted it to.
I understand the AF-C performance was criticized in the video and I'm not sure what the reviewer did or did not do. My Fuji doesn't work like that.
The AF-C performance could be big compromise of the Fuji that drove the overall design. Maybe Fuji had to make smaller, lighter, thinner elements so they can focus quicker. Yeah, I'd give up a few lp/mm for that kind of performance. If your subject is pretty much at infinity and panning across then of course the Pentax system wins hands down if the frame rate suits you.
A more interesting comparison I'm working on is with recent Sony's 200 - 600mm G lens. That lens is huge and heavy. It even has it's own strap hooks! The copy I have feels very similar to the Pentax design. It has a huge foot and well damped controls. Someone at Sony must of looked at the Pentax lens and said, "Oooo! We need some of those in E-mount!"
Perhaps a more relevant comparison would be the Sony 100-400mm lens. It's closer to the 150-450 in zoom range.