> a comprehensive definition of quality teaching
Oh, the irony! Quality by it's very nature cannot be quantified. Not unless you give a very narrow definition of quality, which defeats the point of quality in the first place.
I had a wonderful teacher once who would frequently go "off script" and talk about things. He talked about the beauty in numbers, the elegance of many theorems, the evolution of knowledge. This likely had no bearing on my graduation, but has had a huge influence in my life in making me appreciate and learn new things. A teacher can only teach so many things, but if they instill a desire to learn, the student will learn much more that the teacher could ever teach. How in the world will you quantify that?
If your provost was a hopeless old dolt who got giddy from reading this year's book on leadership excellence or something, there was hope. One could use appeal to logic and reason in such a case to show how quantifying teaching could be detrimental to improving teaching. But I would give them the benefit of doubt that they know all this. There is most likely an incentive structure at play. Job security, career growth, relevance, are all the usual suspects. What helps in such cases is to understand their real objectives and offering alternatives that are still aligned with their incentives. They most likely care more about the outcome than the process.
These incentive structures chain all the way to the top and Unless the absolute authority on top has good interests at heart and can think in a mature way, it's very difficult. You also definitely don't want to do this alone and want to have numbers on your side. Even if you don't have your way in the end, letting people know that the collective opinion is not in their favour will make them take heed.
My take: Pushing back directly against this kind of thing is dangerous and difficult. In a normal environment it will get you driven out, probably to a place that's better. Tenure, on the other hand, can be a trap which will allow them to do things to you much worse than firing you.
In martial arts I was taught "don't be first, don't be last" and that "the nail that sticks out gets the hammer". If you can manage to be within a standard deviation of the mean somebody else will be the victim or be the nucleus of resistance.
Plan B: If you can't beat them, join them. Can you get on this committee? It seems like you have some insight into your own strengths and weaknesses and those and other professors. If you think a professor can be a great professor by helping the strongest students and other professors are great by helping weaker students there should be an evaluation system that recognizes that. In fact, if it is recognized the school can do a better job of matching professors to students and classes that will help students where they are.