Except that the time it takes to set up the project is negligible compared to actually developing it. So if it takes you 5 minutes and me 5 hours to have a new project up & running, that doesn't really matter in the end.
I’ve done a 1 month MVP on each of these stacks, it’s not just the initial deployment. React is better integrated in Next, and you can get more done faster and simpler. DRF has poor async and is not an ergonomic practice in 2022, Flask requires lots else to build and maintain with weaker integration / community, and if you’re arguing why HTML templates are just as good, well, Fortune 500 and every HN startup has left it behind for good reason.
In one instance you're talking about "HNers making a quick product", and the other you're talking about fortune500s. Two vastly different things with different needs.
I'm also not arguing about the specific tech. It's irrelevant. If I know tech X, choosing tech Y because it's hipper or "faster to set up" helps nothing if it's slower because it's unknown to me.
