The 1/16th Slash is just a big 1/16th scale, just how the Revo is listed as a 1/10 when that is a pretty big 1/10th. I agree that its quite a bit bigger then the 1/18th Desert Truck. I would put the 4wd Slash into like a 1/15th scale or even 1/14th just like how I would put the fullsize REVO into the 1/8th. Maybe they couldn't get smaller still using the normal Revo's design and holding up to the abuse.
Mugen MBX6T - Ninja JX.21 with EB Mods Headbutton, O.S. 2060 Pipe, DX3R, Hitec 7955TG Servos on LiPo
HPI Cup Racer - Murfdogg Synergy 17.5, Tekin RS Pro, 2S 40C 4200mah, DX3R, Sav÷x SC-1251MG Servo