I agree with the octagon scenario, but not with a streetfight. If you're outnumbered, it is not advisable to go to ground. That is when rapid high damage strikes and the ability to dodge, block, or soak hits make you not just a physical weapon but psychological.
By the way, in full traditional muay thai, both quick and prolonged stand-up grappling is trained for.
I never said it was a good idea to go to ground in a street fight - but if you end up there (very possible!), Muay Thai isn’t going to help you technique wise. Conditioning would of course.
BJJ is as often about transitioning to and from, and controlling on the ground fighting - so having both would be pretty solid ‘academically’ probably.
It’s not like if you get jumped in a dark alley by someone they’ll just back off and let you get up if you fall down. Unless they were really stupid anyway.
Same with broken bottles, random street junk used as weapons, knives, multiple opponents, etc.
Which neither are going to teach you much about practically in real life, but better than nothing.
I think I forgot to mention how the best way to win a fight is to not get in one? Haha.
By the way, in full traditional muay thai, both quick and prolonged stand-up grappling is trained for.