I'm not convinced they would just yet. Sittichai would have just as much chance of beating them as they would of beating him under K1 or MT IMO.
Buakaw getting KO'ed by Sato didn't effect how I viewed Buakaw. Petro getting KO'ed by Ristie didn't effect how I viewed Petro and definitely Sittichai losing a close decision to Superbon hasn't changed how I view Sittichai. Instead its changed how I view Superbon.
What stands out to me with sittichai is even when he losses he doesn't lose badly. All his L's in the last 5 years have been either close or controversial. We've never seen him clearly beat or KO'ed like we've seen with Buakaw, Yod, Petro and even Superbon so to say Buakaw and Yod would definitely beat him under MT is ignorant. They COULD beat him but not definitely.