Hi
I passed ABRSM grade 8 theory (as well as 5 & 7) many decades ago. Also as part of my BA degree with the Open University I did a music diploma which was at honours degree level. All have contributed to my understanding, though much of the detail has been forgotten, as my diploma was completed in 2004, and my grade 8 at least 10 years before that.
The theory that has most contributed to my playing, is understanding chord structures. What improvising ability I have comes from that work, that I put over a period of several years from the age of about 19 in the early 1980s.
Starting with recognising that F A C is an F major triad to fairly advanced Jazz chords. If you say to me, play a Dm7 chord, I don't have to think, I can instantly play it on the Piano in either hand, or both, in different inversions on the fly. And I can improvise based on that chord and patterns based on it, that I've developed over the decades.
I've detailed this many times before so won't repeat further detail here now.
Cheers