It's already hard enough to get consistent behavior with a fixed model

If we need to save money we will switch to a cheaper model and adapt our prompts for that

If we are going more for quality we'll use and more expensive model and adapt our prompts for that

I fail to see any use case where I would want a third party choosing which model we are using at run time...

We are adding a new model this week and I've spent dozens of hours personally evaluating output and making tweaks to make it feasible

Making it sound like models are interchangeable is harmful