Reevaluating career path - no promotion after 6.5 yrs

I was in a similar spot to where you are now - was making below-market and took a pay cut to join an upcoming REPE GP shop with a hybrid role with impressive leadership with the pitch that years down the road, I would end up catching up / surpassing market pay and having a good seat at the firm. The firm ended having lackluster success my first 3 years and I got no where. Continued making bad comp, not getting promoted, unhappy in general. I ended up sticking around because of COVID and we eventually hit our stride, I got promoted, but I'm still struggling to get market comp. I'm close enough now that I might still stick it out, but if I could go back in time I would have left years ago. If you're working for a smaller firm, you just gotta be excited about the founders since they're always going to control everything. If they've been cheap for years already, they're always going to be cheap. I've learned as I got older that some people just have a cheap mindset and others are more generous. The cheap ones are always going to pay you the least they think they can pay you without you leaving. If you prove yourself to be more valuable, they'll raise your pay but still keep you at the bottom end of the range. On the other hand, generous people will just reward their talent without being forced to. It really sucks to have to go to bat for yourself every year just to try to get into the bottom range of "market pay" and I can tell you from experience it will burn you out over time. 

If I were you, I'd just start slowly recruiting until you find the right position even if it takes a couple years. Oh and by the way - when you deliver your notice to leave, almost guaranteed your firm will offer to match the comp as if suddenly things have changed. These kinds of people just suck to work for.