Got the playstore update but still no security patch. All the other Nexus's got security updates. To think I bought the Nexus 6 thinking it would have been first in line for updates but no. I just hope I don't have to sideload and factory reset everytime I want a update.
The Nexus 6P which I should have waited and got instead don't have issues with carrier updates. Carriers don't sell it.
The Nexus devices are the only ones (so far) that have gotten 6.x, so technically, still first in line for updates

If you choose to sideload, you don't need to factory reset really. Personally, I avoid sideloading, and just flash the factory image (skipping userdata) - quick, painless. But not everyone is comfortable doing that.
I suspect the 6P will have the same issues - I think T-Mo recently announced that it was working with Google to make the 6P Band 12 certified. I would not be surprised it they ended up with a separate build (just like the Nexus 6 did). Having said that, The N6 has B12 support and WiFi calling on MRA58K itself (even though it was supposedly not the T-Mo specific build)