No, they should not change the model at all when you select the model.
No improvements to prompts, tooling, harness between model releases? Is this really what you want? I don't think you've thought this through at all.
They should let you use your subscription with your own harness. Until they do, you're just borrowing someone else's workflow, which is liable and likely to change whenever the fellas over at Anthropic get a wild hair and decide to introduce a new experiment.
Well.. that's a totally different argument.
Please make your substantive points without crossing into swipes or putdowns.