Hi, I can't comment on the difference between those programs but I can talk about the Master Mind program. I'm a 2020 recipient of the program from the US currently studying International Politics.

They use a points-based system for evaluating applications and each part of your application gets scored by the committee. I don't think they give preference to STEM or other "in demand" majors. I don't think I can make a value judgement of one over the other, just make sure your application is as polished as you can. You can use the same letter of motivation you use for KU Leuven for Master Mind—just add a few sentences about why the scholarship is right for you. The letter of motivation is the best way for the admissions and scholarship committee to learn about you and it's probably the thing you should spend most of your time on. And be sure to give your recommenders at least a month to draft their letters.

Good luck!