IMHO 3xts-1400 should be enough. But it would make transmission complicated and expensive.
Also TUSAS has no experience with 3 engines. So they probably did not want to enter unknown territory.
A guy "sequ" from sinodefenceforum made a very good guess about empty weight of MMU.
Let's try to guess MTOW (maximum takeoff weight)
Empty weight = 34.000 libre
Useful Load = 20.000 (İbrahim Sünnetçi sent a tweet about this which I can't find at the moment.)
Fuel Load = 20.000 (We use the same...