I agree that excavation is the most worthwhile. But I do not agree with much else.
Firstly, you should speak for yourself. I will never believe you have polled all the arbitration players and have statistics of what "the majority" think.
I do not completely disagree with your ideas, but I believe you want too many rewards in one place, too easily.
Adding normal rivens to the rewards will just de-value all the rivens people have paid thousands and literally more thousands of plat for. So I see this as a really bad idea.
Adding kuva to the rewards (the arbitration store and the reward rotation drops, I bundle them into "rewards") might work, but the main source for kuva should be Kuva survival and kuva siphon. Doing arbitrations for kuva should suck in comparison.
I have the same thoughts for Endo farm. Why should arbitrations give more endo than Vodyanoi? I do not see any reason to increase endo rewards to make Arbitrations as good as or better than Vodyanoi.
I am divided when it comes to changing the rotation time and setup. But given a choice I would definitly keep the current system over your suggested system. Because you would be getting rewards too quickly.
I was pretty content with the old arbitrations. The main reason being the perma death that kept most of the public game Leeching players (who just want to be carried) away.
Sorry, I can't do easy to read formatting like you. Having a quote of your post took up too much space with my poor skills.
Good job DE!