To be fair though, you typically end up doing that process even when you remain within the OpenAI ecosystem, because they're putting out new (cheaper) models.
For example, a couple weeks ago I migrated a few game mechanics from GPT-4-Turbo to GPT-4o and it caused significant enough issues that I needed to revert them all until I could go back and retune all the prompts, which ended up taking 2-3 days. That's probably about as much time as it would have taken to tune prompts for any other model, especially since I'm using an API that standardizes format/structure across whatever model I select (as simple as a dropdown) and lets me just focus on prompt messages independent of which LLM they're going to.