@shiframeir, you are missing a few points in the Rambam
1. Just because drashos are overridable by later chachamim - it's not that the chacham can make up whatever he wants. Ein l'chacham ela mah she'einav ro'os - but he has to honestly see it and disagree with the drasha of the previous generations
2. Just because every generation paskens things the way that they see them, doesn't make the din any less of a din d'oraisa and make it any less from Sinai. It just means that there was no specific mesorah saying that it's a halacha l'moshe misinai/peirush mekubal from Sinai.
3. We can't change these drashos any more (see the chazon ish regarding trei alaphim torah).
I don't think the Rambam is non-standard thought which has been discovered by contrarians. I think the way people portray it might not be accurate, but I don't think anyone will tell you that the rambam in hakdama to peirush hamishnayos is non standard thought. And it is very basic knowledge to have.
See the Brisker Rav al Hatorah on megilas rus for an awesome pshat in the whole back and forth between Boaz and the goel based on the Rambam's mentioned.
Oy, please dont bring up Boaz, I will never get pshat there (but for more fun, check out the amazing Tzitz Eliezer that goes through alot of the sugya too).
1. of course. but drasha is not purely based on a cold read, but clearly cannot help but take experiences and other human factors into account. Just as we paskened mamzer vadai and other drashos with clear conceptual framework underlying, would not be unheard of to work it here (upon consensus, and going back to a more simple read).
2. I agree it doesnt make the din any less of a "Deoraisah" but the din is NOT NECESSARILY from Sinai (though tools provided then may have been used). the distinction may not matter in practice in most instances, but there is reason to distinguish due to ability to change and the inherent valuation we all have to law passed from Hashem to us vs by a rabbi at a certain time that is subject to change. TO be clear, if it is a hlm or a pierush of the torah from sinai (category 1 as noted by R Aygart), then it would seem that indeed we could never change the law (subject to Shev Ve'al Taaseh exceptions, which would not change law anyway). the question is whether indeed these specific rules were part of the mesorah from sinai. and that just is not clear (a problem in general with the Rambam's approach).
3. with all due respect to the great chazon ish, he is not the first nor the last to question whether the Rambam's allowance for changes by later beis dins to drashos to apply (see what i am sure was a great Kovetz hearos on why rov yisroel couldnt go back on accepting the bavli as binding, and going further back to the mechaber/kesef mishna etc). I would ask how the Chazon ish could go ahead and change the status quo of being able to go back, and if he did rule that u cant anymore (or cite someone who said so), can't we go back on that too?