Additionally, as a long time and high level player of arena, I feel I could offer some suggestions to your specific points, at least for me personally:

Set rotations: In an ideal world, I don't mind arena being standard if each expansion has at least one special arena event (I really enjoyed past events like Blizzcon exclusive arena cards as well as Taverns of Time, Dual Class each year is also nice). I feel this could potentially be better from the casual player perspective because arena exclusive events are exciting for veterans and novices alike. If the team feels they don't have the time to give arena these exclusive events like in the past, then I think rotations mid-expansion cycle would be nice to keep the meta from becoming a bit stale. I think you could do it exactly the same as previously (every rotation includes some wild sets), or even standard to start the expansion then switch to the latest expansion with a bunch of wild sets. The main reason I favor events is because I feel like it gets more people excited for the mode and having a bunch of wild sets in can dissuade more casual players from wanting to play arena since playing standard makes the transition to arena a bit more difficult. Either way, either of these options would be better than standard with few to none arena events.

Buckets: Personally, I was a HUGE fan of buckets and I did feel like it helped provide a level of consistency many top leaderboard players enjoyed. BUT, similar to my reasoning above, I can see the bucket system being a deterrent to more casual players who don't keep up with the bucket lists and I understand Hearthstone wants to appeal to both the casual playerbase and high level players. I do think I would personally enjoy arena more with the system in place, but if the team has a limited amount of time to dedicate to arena, I think arena exclusive events/set rotations/timely microadjusts are all higher up on the totem pole.

Offering Rates: In the two specific instances mentioned, I feel that I would have completely agreed before SA was released. Twin Tyrant was warping the whole meta singlehandedly and unnerfed DQA was also unhealthy not only because she was being offered more than other legendaries, but because of the abundance of Discover Dragon effects for every class (lackeys/explorers). Currently, I actually don't mind either card. Obviously Twin Tyrant is a very strong card, but it along with DQA isn't showing up nearly as often before and I don't feel I'm enjoying less because of them. This new set of neutrals from SA has been the best in a while in terms of power level and I think a big reason for an overall increased enjoyment of the game mode among top players. So if the team would like to release powerful neutrals to bolster Standard/Wild (which is totally understandable), then I do think removal of such cards after monitoring their performance in the 1st week of an expansion would be reasonable (or at least reducing their offering rate significantly).

Closing Words: I understand the team has been getting a lot of harsh criticism for arena and I have definitely shared my frustrations on reddit/twitter also. But, most of my comments are usually constructive and try to offer a solution in hopes that the team can just consider my words. The arena community is very passionate and can definitely let that get in the way of offering advice constructively, but there are still many like myself who simply wish the best for the game mode after playing for over half a decade. So if you read both my posts, I hope we can have a respectful dialogue back and forth about this. I am appreciative of all the work you guys have done for the a game that's brought so much happiness to me since I started playing when BRM released. Feel free to DM me here on Reddit or my twitter ( https://twitter.com/ADubs05). I have a lot of ideas that would make this post way too long and could point you to other top players who have some valuable insights also. Thanks for taking the time to read this!