Flat out speed is essentially what Geekbench ST is measuring. MT is measuring something more akin to towing capacity, where some people might whine about wanting to see numbers for "what's the heaviest load I can tow over level ground". Even though in the real world people are towing stuff up (and down!) mountains, in rain or ice, in 110F or -40F, etc. and the numbers they would arrive it for max towing capacity are far lower than the idealized numbers that would be reported by Geekbench 5 MT equivalent for towing capacity.
The GB5 MT test for towing would probably be something like tying together trailers loaded with scrap iron and towing them down an airport runway. Look this F350 can tow 200,000 lbs, yay! And after people criticize it as unrealistic someone would claim that test approximates their real world use of towing a few trailers full of soybeans down a flat farm road to the grain elevator.