I agree with pretty much everything you said here. A few comments though.

I do, however, have a major issue with the SBD conversion function being taken off of the flagship site, steemit.com.

This was done to prevent users from using it unknowingly when SBD is above $1 USD and losing money. Perhaps a warning popup while it is over $1 USD would been better option, but users would still do it anyway unaware of the loses in some cases significant. In fact 20,000 SBD was converted at ~$7 USD SBD price, for a great loss and the main reason this was changed.

While SBD is near $1 now, I don't think it is pegged and just following Steem which is also near $1. Even now using the conversion would be a bad financial move as you would lose about 3% right now, and likely more over a 3.5 period. But I do agree the lack of this functionality from the web UI is not good. It is still possible though if you are technically inclined.

20-second comment limit reduced to 3 seconds

The core idea behind this change is no legitimate user should be throttled under "normal" and "reasonable" use. I have hit this 20-second limit many times. I read relatively fast but not a super speed reader or anything and I can hit this limit going through comments and commenting one interesting ones. It doesn't happen a ton, enough that I get frustrated, but I have run into it. I hope the RC changes will curb the ability to abuse this but I have a feeling it won't be a positive change in the end.

With a seven-day payout and a lack of voting and engagement on older posts, I would rather see a cool-down period of 3.5 days.

I honestly would like to see longer payout window. At least as an option for some forms of content. I am a big believer in evergreen content, content you put a lot of time into (video, tutorials, web shows, high-quality content) that is referenced and engaged on for weeks or months later should be able to be rewarded. I have tutorial/information posts that are 6-8 months old I still frequently get comments on thanking me for a helpful post. But I am more concerned with things like Web Shows, high production tv like video content, development projects, and other similar forms of content. Some of these have extremely high labor requirements to produce and it is difficult to justify when you have a small window you can be rewarded for it. Many YouTube channels depend on monetization on videos that get paid out for years. The payout wouldn't be a single payout, but something like a weekly payout. To do this though would require major improvements in discoverability. I'd add though most content on Steem wouldn't deserve a long payout window so there is that.

I would have liked to see more big improvements for 1.5+ years of work and I agree would like to see more hardforks and fewer changes in each. It becomes you like this and this but not that but you got to take 20 changes along with it.