Alternatives (besides Garmin) to the Venu Sq2?

Like I said in a previous post, I really want to keep the Venu Sq2 I've purchased two days ago.

It fits my wrist nicely, it's light, I like the Garmin sleep reports, and it has great battery life!

But I can't ignore the fact that I've paid more than 250 $/EUR for something that doesn't allow me to upload a simple app or watch face...

So...

What alternatives are out there? 

I'd like to stay away from Garmin after this problem, because I don't trust their ability to maintain a proper app ecosystem.
Even a cheap crappy tracker that I purchased last year from Huawei could transfer watch faces instantly!

1. Something with equally good battery life (at least a few days, preferably a whole week);

2. Something not overtly big and thick, like most of the other Garmin offerings;

3. Preferably a square/rectangular form factor, though that is open for debate;

4. Above all, something that syncs correctly.


Thanks!