I have a theory about this from spending decades as someone I am not (then again, I am INFP so I def need a sense of purpose, as well as a bunch of spiritual placements, so that might just be me).
Find yourself first, then fix issues. Or rather, focus your MAJOR sub around your personality to gel nice, and use the other 2 slots to add skills that you need.
For example, here is how I PLAN to run subs going forward.
Stark seems to run VERY well for me, although I am not E. But the sub will likely make me just an introvert that is public. I will run it with Chosen and RM at some point, to see which one becomes my actual major sub.
This then I will run for quite a while as the Major slot.
Then I add 2 subs that either are result enhancers (like ME) or add things I need (like more money, or sexual).
MAJOR: Stark
Result Enhancer: ME
Skill: Primal Seduction for the sexual edge
Then after 21 days, I rotate
MAJOR: Stark or RM
Result Enhancer: Limitless, QL, etc
Skill: RICH
Rinse, repeat.
I mean, this is how I built my customs. The Major cores to aid the personality I have, supercharged, result enhancers to maximize, and a bunch of skills I need, like money.
I think this makes sense to run the actual stack similar.
On another note, Astrology also helps you a lot to find a sub that works for you. But itās not easy to learn that 
You can also use Jungians Archetypes if you want and match them to the subs. But I do think, first running something close to your personality is helpful.
And then thereās healing, which is its own thing 