Earlier quoted context omitted.
"This prize isn’t too highly regarded." [By whom?] "The physics prize has mostly consisted of string theorists giving it to their friends in the field." Firsty, the Breakthrough Prize is given in Life Sciences, Mathematics and Fundamental Physics. This post is about the Breakthrough Prize in Mathematics. As for Fundamental Physics, apart from 2019 (special) for supergravity, it doesn't seem to go to string theorists:…
Whom was me and others in the physics department I was associated with. You can find more discussions on the prize on the not even wrong blog https://www.math.columbia.edu/~woit/wordpress/?p=8958
"One thing that strikes me about these things is that the situation with the physics prize has changed dramatically since the first three years, when they went mostly to string theorists. Having a heavily promoted much larger cash prize than the Nobel, given largely to theorists for ideas many of which haven’t worked out, raised obvious questions about the wisdom of the whole thing. The last two years have seen a 180 degree turn, with the prizes going to experimentalists for successful experimental results. Even better, there has been an unusual emphasis on making an award to entire experimental collaborations, not just a small number of “great men” identified as collaboration leaders or spokespersons. I don’t know of any other major prizes that do this. The lack of an experimental Nobel for the Higgs discovery is one reflection of that problem, it’s great that the Breakthrough Prize people are doing something about it."[0]
Basically, we have two criticized recent physics awards (2019 special and 2017) and several in the very beginning. That still doesn't qualify as 'mostly'.