The more I think about it, the more nervous I am. Bixby gets a bad rap, but I actually like it and prefer it over Google assistant. It annoys me to no end that I am forced to use Google assistant on Android auto as I have all my privacy settings turned off for Google, I can't even make a phone call or listen to a text. Samsung health is much nicer also, I'm hoping Google really just copies Samsung. Samsung really did a fine job with Tizen on their watches.
I've experienced Wear OS's version of Google Assistant. If anyone hates Bixby and expects the Assistant to be like it is on their phones, forget it. It's 1/3 functional at best. Fails more often than one would expect. It can't do half of what Bixby can do. I think of Bixby more as a voice control for your phone, not as a replacement for Assistant (thankfully on phones, you have both! And neither conflict with each other, and both respond to their respective wake words via my Buds as well). Bixby can pretty much avoid a touchscreen full of finger prints. It really comes in handy to text, call, or do functional things on the phone (Hi Bixby, Open Galaxy Store and install Megapolis). I've wanted that level of control since watching Star Trek. I always hated grimy touchscreens or viewing content through them. So in that respect Bixby works quite well.
On my Watch 3, it can do similar functional things such as go back to the main screen, open apps, text, call, turn on water lock mode, pause or play or change volume of music on the phone, and far more. It's actually more feature-rich than it was on the 2018 Watch.
On Wear OS, Assistant is all you get (unless Samsung gives us both). Not only is Wear OS a battery hog (get used to charging twice daily), the Assistant is pretty broken. Even more so since Play Music integration was removed (there is no Wear OS YouTube Music app like there is on Apple Watch and no way to control it from Assistant on the watch) You cannot add tracks to play from the watch at all since there is no native music player once Play Music got axed (thank you very much, Google). Apps such as Spotify can't play offline via watch.
Assistant can't start navigation anymore (it tries, fails, and just says 'couldn't start navigation'). It does get the navigation going on the phone however, but you have to tap 'start' to get it to work, which means pulling your phone out, unlocking it, and tapping the screen. Assistant used to be able to text or call, although it was not hands-free. It'd know to open messages (Android Messages, and I'm guessing Google Assistant can't work with Samsung's app) and it'd dictate it, but you had to actually tap 'send message' yourself. Bixby can do the entire thing hands-free.
Today, either feature is broken. It just shows a sad cloud icon saying 'Can't connect to your phone' which is its universal error for a bad connection or a misinterpreted command. Now, on Wear 1.1, it was all great. It was a far more viable platform and had potential until Google rebranded and changed it.
Functionally, Google Assistant can't do much other than open apps, dictate text, and install things from Play Store. It's not at all as good as it is on the phones, or speakers.
I don't know why Samsung thought they needed to go Wear OS. The rumor has been a thing since the Samsung Gear S3, so I hope it's still just that. Google has pretty much abandoned Wear OS as a platform, and I'm guessing if Samsung does try using it, they would have to fork it like a Kindle tablet does. I certainly don't want Play Store or other Google apps on my watch. That's a nightmare I would never want to revisit--it was really that bad!