Also, cloud providers can make a huge difference too. They can be optimized for one type of tech and not the other one. I found that deploying a telegram bot in a Cloudflare worker was much more responsive than deploying it as an Azure App Service or in Render.

Also, I don't love MongoDB and would much rather use PostgreSQL and never had issues with 10K users through my API. However, the difference in price between 15K and 3K makes MongoDB a win on this.... as it is a 5x multiplier and as a solo developer it makes a world of difference.