The s3 is HUGE compared to the AW, even the 42mm. It also runs Tizen, which has only a fraction of the apps iOS and android have. I'm also hesitant on the heart rate sensor as I've always found Samsung to have poor ones, but never tested the S3. I know my AW HR sensor is pretty darn excellent.
I am late to this thread, but wanted to throw you a different idea. I wore the Apple Watch gen 0 every day for 2 years until I got the Note 8. I was very concerned about continuing to have a smartwatch, because I perceived that Apple Watch was so much better. I would never have gone to the extent that you have... to have a dedicated iPhone just to manage the watch.
I went with the Gear S3 Frontier, having never touched one other than 5 minutes one time in a Best Buy. I am delighted with the switch from AW to S3.
There are two areas that the AW is better - 1) complications, which are cool with integrating apps into watch faces, and 2) more 3rd party apps. When I evaluated my usage of AW, I did have some 3rd party apps, but none of them did I use a lot, and in all cases they weren't really anything that I had to have vs. just using my phone. They were novelty more than anything else.
For everything else, I prefer the S3. First, the UI and navigation is way more intuitive, and the rotating dial is so much better. I use the watch in the gym, and with sweaty hands I hated the AW. I can use the S3 while running no problem. I also like that it looks like a real watch. It is not small, but its also similar size to regular watches. My daughter, who isn't very big, has a G-Shock and a Michael Kors that look almost identical in every way to the S3 Frontier. I like that there are thousands of watch faces. that add to that look and keep it fresh. Watch bands... uses regular ones.
For the gym, I can take just the watch now. I use Spotify to put my music on there and use the Samsung fitness app to do the rest. I've gotten texts and calls while at the gym and they transfer fine. I love the experience compared to AW.
For sleeping, I wear the S3 ... never wore the AW. It automatically tracks my sleep. I don't have to do anything. I can also turn off the alarm on my Note 8 from the watch.
For payments, the S3 has Samsung Pay that works in way more places than Apple Pay. I've started just leaving my phone in the car because the watch works better for payments, and I an communicate. Unlike AW, I can type a text on a keyboard on the watch. Phone calls are also clear.
Your list of things in the original post were all built in native functions. You didn't mention any apps. I would highly recommend you give the Gear S3 a try.
