|the difference in the 2nd and 3rd gear synchro design from pre-98 to post-98 FS/RS5R30A. It is debatable whether this change was to improve shifting speed or quality, but I don't believe there could be a change in power handling capability between either version.
I imagine there may be some aftermarket offerings for pre-98 replacement 2nd and 3rd syncro brass rings, but a side-effect problem of worn brass rings is then the strut teeth on the gears and sliders get narfed all to hell from people just trying to jam it into gear. Once that happens, there's no new brass ring that will fix it... the gears and sliders also need to be replaced - and the only 2nd and 3rd gears/sliders that exist in new form for this transmission are '98+ versions.
Or you can disassemble multiple pre-98 transmissions to sort out all the best parts for a rebuild. This is what the guy in your video is doing. He may seem like a manual transmission genius, but all he's doing is selectively identifying all of the parts that are too worn out and replacing with parts that are not.
Aside from some gear wear problems that happened awhile back, I think what's causing the perceived shifting/noise issues is people's expectations that their new '98+ transmission is a "performance" transmission simply because it works in a Z32, and can therefore be power-shifted without mercy. In reality, the '98+ transmission is not a performance transmission, rather it is a workhorse - it was used in countless Pathfinders, Xterras, and Frontiers long after the Z32.