Main thing is if working for you that's what counts. My work Gyuto's always did all my sharpening on Medium stones.
Single Bevels Polishing stones. Yanagiba's would sharpen after a heavy fish day on a 5K, later on got a Kitayama 8K. The SB's you are taking from sharp to razor edges. Don't need to go to lower grits unless with wear moving up bevel line.
You are correct with thin Sugi's over sharpening will wear them down, its a trade off when you wear them out get another one.
These days with high hrt. steel gyuto's like to finish off on 4K. Just personal preference, really no need to take gyuto's past medium stones.
Definitely.
I was a few deep after work last night so I probably didn't do the best job explaining things.
My Ginga suji was a real eureka moment for me when I originally got it. Just how it cut food and the edge retention it had... I road it hard on poly boards for about two weeks before even feeling the need to touch up the edge. When it arrived it had no visible bevel and so I was unsure how to go about sharpening it. Looking online I saw that in the past on KF that KCMA said with lasers (like a Suisin IH) he liked to keep the almost non-existent factory bevel and would only polish the blade face with higher grit stones, similar to what TheDispossessed was talking about. I decided to go about sharpening it like I do all my other knives - set a (low) angle and make a new bevel. It still performs well but it doesn't have the same cutting ability and retention like it did when I first got it. Which is strange because I haven't had that experience with any of my other knives - including a Ginga gyuto.