Scramblers are gone for a reason Strong Bad. 19" wheels were NOT better in the desert. Not even close. It is what was used back in the day of those pics. Once DIRT bikes of all types went to 21" they never went back. NO ONE uses a 19" in the desert. If they were better they would use it. Johnny Campbell would be using one, Mouse McCoy....
19" wheels on your bigger ADV bikes are pure there as a comprimise and NOT because they are BETTER in the dirt.
The comments about picking the right tool for your job is exactly right. If you are gonna ride alot of hiway and some dirt gravel roads a 19 is BEST...for that. If you are gonna ride alot of dirt, sand, mud, and loose stuff and 21" is it.
there is NO floating effect on a 19" wheel. As I stated before, until you go to a really fat tire it is not effective. Look at all sand toys. they use a ribbed front not to float but to rudder basically.
21" suck on long hiway stuff. Not great wear, not that that is impossible but no one I know make a long lasting 21" knobby. very little contact patch because of its narrow width and generally knobbies minimize contact patches as well.
As for the 23" on the Hondas back when, they ran them on the CR125 in 1979 I think as well as the early 80s xl500s. I had one...It was that TOO A POINT thing. The 23" was a bit too far. Not neccesary and made the steering heavy. It never took off and tire were then and still tough to find and thus expensive.
In the early 2000s Mike Larocco tried running a 20" front tire for SX that was a bit wider thinking it would stick better and there are no big rocks in SX but it just did not work either. It did not carve the same in ruts.....
21" in dirt. 17" on tar, 19" if tar dominated but occasional dirt.
it is easier to ask for forgiveness than permission