Someone mentioned this earlier, but the "band steering" thing is most likely a router thing. I believe each router out there has different requirements as to when it "steers" a device to the 2.4ghz network, and as the previous poster said, can be customize-able. I've had this issue for quite some time on many devices, including previous iPhones. To the point where I just disable it and keep separate networks (2.4, 5ghz-1 and 5ghz-2) and then only add the network I want the device on. Band steering has always been pretty flaky for me.
Also, my daughter picked up the XS last night, so I'll be interested to hear if she's seen anything specific as far as LTE, speeds and dropping back connections, etc. My guess is no, but she may not notice unless it's pointed out specifically.