With QF->UA, you sitll go via connections, but then have to get to T7 - which is either wait for the shuttle bus, or a 15-20min walk outside.. all fine if one enjoys that - catching the shuttle bus may save a bit of time, but it will stop at T4/5/6 first.
One could always use the connecting security at TBIT (as above) to re-clear and go through the airside connector, but it's still a 20-25 minute walk to T7 (I've done this a number of times - and I'm a fairly fast walker) so it's not trivial to walk.
And again, sometimes arriving ~0630ish I've been in the lounge by 0730 having a shower and could catch a UA (or QF/AA) connecting flight east if need be. Other times, it's been a mess and I've still been trying to get through CBP at 0800. Everyone's mileage will vary.