One of the most unfortunate things in the US is locked bootloaders. AT&T has even started whitelisting phones for Wifi Calling and VoLTE. And with 3g shutting down, it means international phone variants won't work at all on the network, regardless of the underlying band support. Many companies, including Samsung don't allow you to unlock your bootloader to root your phone even if you bought it outright. I found that midrange phones are now the best option if you want things like AOSP. The only true flagship left, that I know of, with a headphone jack and sd card and good rooting support is the Sony Xperia phones.