your observation is correct. Not only is punching only one of 4 types of stikes allowed in Muay Thai, in competition, punches landed score less point than kicks, knees and elbows landed. Muay Thai has a very different scoring system.
Obviously an art that allows all limbs to strike, won't be as good with just two limbs, compared to a sport that not only restricts striking to two limbs, but also limits HOW you can use them to strike.
In Boxing you can only punch with the front of your knuckles, while Muay Thai allows backfists, and even hammer fists I believe, which when allowed totally change the potential dynamic of punching.
But you don't think a dirty boxer who was allowed to throw elbows and kicks and clinch that he wouldn't do very well in a match with a muay Thai dude?
Yes he could do very well, but would still be at a disadvantage on paper. Where is this boxer learning to knee, elbow and clinch anyways? Also, don't forget about trips/takedowns from the clinch, where is the boxer learning those?
I do agree, that having a solid foundation of boxing is very important, but you need muay thai training to really learn how to deal with kicks coming at you, and deal with the clinch in a situation where the ref doesn't immediately separate you.
The sort of stylistic/strategic approach you are speaking of though, I do think is a good idea, but to implement it effectively you would want to cross train both arts IMO.
