You can tell a startup is focusing on the wrong thing when: They're using the 'newest', most obscure, programming language or frameworks available because it's the 'best' for some unscientific reason.
Instantly I hear the argument "Yah, but if we need to scale, we don't want to re-write." Ok, you're going to rewrite anyway. Right now your problem is producing quality code that additional people can onboard themselves with. Chances are you can produce something very practical using plain GET/POST operations and gradually add more interactivity on the client side if you prove your product out.
The stem of my rant is this: Recently I was thinking about picking up some side work for extra $. The company I was interviewing with described their front end team as struggling to keep pace and needed some temporary help. The product is under NDA, so let's just say it's a shared calendar. Their stack was insane: 18 different javascript frameworks, required a certain version of Node.js to "compile" to ES6, then another to run it in your browser, and the stylesheets were written in some other obscure language. In the second interview, I told the product manager I think he's been had: the reason your front end team is struggling is because they're not being practical, they're busy with shiny toys. He said he had a feeling, but given his situation he didn't have much of a choice but to continue. He thanked me for being honest and said he understood if I wasn't interested anymore.
Anyway, there's a lot of really "cool" stuff to get distracted by as developers. I think a lot of us need to sober up and really meditate on the phrase "do the simplest thing that could possibly work".