There's already a (non-public) beta firmware which has an upgraded Broadcom SDK.
Also if you updated to 3.0.0.4.378_412x, make sure you do either a factory default reset, or at least go to the Smart Connect page, and click on the button at the bottom to reset rules to default values. I know some steering values were adjusted in the latest firmware.
Netgear does not have any issue because their band steering is dumbed down to an extreme - they use their own very basic band steering daemon rather than use Broadcom's full-featured one. The sweet spot however probably lies somewhere in the middle between these two extreme approaches.
I suspect that, over time, users will experiment with these settings, and start posting their own recommended settrings to use instead of those set by Asus.