"Uploading the entire gallery" is exactly what Google Photos and iCloud do. Samsung tried its hardest to get me to agree with it too. Even OneDrive tried to pull a fast one on me at some point. It's par for the course for modern operating systems.
I bought Xiaomi with the hope of it becoming popular enough to get LineageOS support, but a month after I bought my phone they released a slightly different version that actually became a hit so I was stuck with MIUI. The hardware in my phone was about equivalent with phones twice the price at the time and even features an IR blaster, which no other brands seem to do anymore, so it was worth a try.
If you read the T&C and deny the prompts, it's not that bad. You need to go through every Mi app's settings and disable ads, but after that you can use them just fine. They're great phones for the money if you're willing to deal with denying the stupid prompts. I very much knew what I was getting into, I just lost the LineageOS gamble. They come with Google Play so you can just download Google Drive/Photos/Files/Dialer/whatever and use the phone like any other.
I wouldn't recommend them to the average user, though they're often still a better deal than most of their competitors in terms of value per dollar.
Luckily, another custom ROM project picked up my phone and I'm pretty happy with it now. They're great phones for tech savvy people looking to save hundreds of dollars if you've got an hour or two to clean up the crap.