USDs flex mostly at the top of the lower tube. When that (momentarily) bent tube tries to move through the bushes, it binds up.
RWU forks flex mostly just below the lower triple clamp - well away from any bushes. Even though there's more flex, it's doesn't cause binding.
The second year of Japanese USDs deliberately reduced the stiffness of the upper leg to minimise the problem, but all of the 40 and 41mm USDs are pretty crap because of it.
USDs only really began to work properly when they got to 46mm.
That said, some of the mid-00s KTMs with 48mm forks have three bushes in each fork leg, and they work like rubbish. The fix is to remove one of the bushes so the flex doesn't cause bind.
Worth mentioning that Geoff Ballard (and Jess Gardiner) run TTR RWUs on WRFs, and that (in 2007ish) Ben Grabham rated the XR250 as much better in rocks than the team CRFs.
Everything of this era has way too soft springs, unless you weigh 40kg... (Hondas are the worst, FWIW). Definitely the first thing to upgrade.
