I think it kind of depends on what you're familiar with. If you're a rails dev and you can build something crazy fast with rails vs anything else I'd just do that. If you're used to working in event-driven microservices environments, then do that. I'm working in an environment using node microservices, mysql, rabbitmq, with k8s and it works really well. I wouldn't say we're _faster_ because of k8s, but k8s really helps us move quickly once we get a service deployed to the cluster.

I'm also working on a start up, and chose to start with heroku and a PHP monolith (with a handful of microservices to do some of the heavy lifting) because those are the things that allow me to move fast. If we ever make some money and the product does find market fit, we'd probably move to something like k8s, but it definitely isn't a part of the early stages for us. YMMV /shrug