I'm kinda curious too? ╮( ̄▽ ̄)╭ The whole "Achieving ML/FL and unachieving MC" is a very common trope, but their aren't many that display it realistically?
A few recs if you don't read them already:
Straight:
Tears on a Withered Flower:
FL in unachieving and often ashamed, ML is highly achieving/well off and hides it
BL:
Unsleep:
ML is well off an achieving well but thinks nothing of it/not a main point in the plot right now, but MC feels like an underachiever
The Pizza Delivery Man and The Gold Palace:
Rich ML x Poorer MC trope but a little different + nontypical ML. Them being on opposite ends of life becomes a main focus for a while.
Not so related but kinda related:
(BL) Yang Il-woo and I:
Not so much about achieving/not achieving but there's a power imbalance involving MC/not much is known yet cause it's still decently new.
These probably aren't EXACTLY what you're looking for, but I'll keep hunting!

Guys I have a really hard recs request, I don't know if it even exists. A sorta realistic? romance story (bl, shoujo,...) with a high achieving ml/fl, and the mc that is basically the opposite and is ashamed of never having achieved anything in their life, ashamed when comparing themselfs to ml, doesn't feel worthy and so on...