So I picked up a 3A USB charger from Officeworks, this thing is actually QC3.0 rated although I'm only vaguely aware of the QC3.0 vs USB PD and don't think that either actually come into play with this powerbank. In any case, it can output 5V @ 3A (it says up to 18W which is actually slightly higher than that it's got a little headroom).
In any case it seems to happily charge up the battery while the battery is also charging two devices without breaking a sweat or getting anywhere near as warm at the 1.5A job I was using last week was.
Performance wise the powerbank did a great job charging up devices on the go. Charging up my iPhone 6+ while running Nav (so GPS + Data + full brightness) seemed to happen far more quickly than I would have expected... not that I was scientific in anyway so it could be 100% placebo effect. But it did work.
Handing the charger to my son (who will sit quietly all day on his phone if you let him playing battery intensive games) saw it come back with 50% power at the end of the day, which also included about 2 Hours or so of keeping my phone at 100% while driving using the nav). Not bad at all.
It's bigger than most and heavier but it does what it says on the box very nicely.