I'm curious what the author's take on scale.ai is since he was considering building an ml-ops / data labeling company and they seem to be the most successful startup in that space.
I'm going through something similar at a much smaller scale (startup CTO of 2 years, not much growth). It's been enough to make me want to quit software engineering altogether. It sucks.
At least your company is growing and you know that you are a decent developer.
Maybe you can take a sabbatical. Talk to your partner if you are on good terms. Make sure to explore your options.
Hope you find a way to move forward and regain your confidence.