Combat sambo allows kicks. That and the footwork of boxing comes handy when you are trying to evade and counter punch. They are good combination. This would be my thought too : As a kid start in Sambo to learn throws, some submissions and leg locks early plus start boxing so they have a long time to build natural good boxing technique. Once an adult move to bjj to refine/add submissions to their sambo and muay thai to add kicking, knees and elbows (plus toughness). Should then have a fighter who has good throws/takedowns, good submissions and good striking. Then you find out they are chinny and it all goes out the window!!