The algolia api has more bulk operations, so you can get more than one response per api request. Also if you look around, there are some datasets where people have downloaded all the HN API json responses, and have made them available, so you could use those for local development and testing.

As far as ethics go, it's probably better to use the API than scraping. Sure you're making more requests, but I think the firebase servers and cdn have far more ability to handle a lot of requests than the HN server does. If having that many requests would put firebase out in any significant way, then I'm sure they would put a query load limit on the HN api.