Martial arts to get built

[u/Terranam1]

Hi Im 21 and got a little bit of muscle and a little bit of fat and do MUAY THAI on rare occasion (to learn how to fight and 2 to get built); I ask my instructors if there are any exercises I can do outside of class to get better and they shrug it off or say hit the heavy bag for 30 minutes. Anyway I was wondering what martial art would get me built the quickest or just built in general? And is the instructor advice sound

[u/smackadoodledo]

Honestly Muay Thai isn’t gonna build that much visible muscle at all, if you want to get bigger just lift weights as much or more than you train Muay thai