I haven't driven a hybrid but my gut tells me the engine is too small for the vehicle weight.
Mileage is low in the hybrid partly because of a small engine but that's because it had other problems which act against the engine. When running with heat on or a/c because the engine has to always run. There is no electric water pump. There is no electric compressor. This causes the engine to run almost always under many circumstances. When driven with no heat or a/c it actually gets sticker mpg. Now, when driven hard, the engine revs so darn high because it's small that mpg is bad even with no heat and a/c usage. Also, the battery and electric motor are quite small for a vehicle this large.
What they need to truly address concerns of low mpg on the hybrid would require the engineers to build 'a better hybrid' and vehicles already built cannot be 'fixed' so it's great they are getting engineers involved for maybe future generations right now, they can't do much to address concerns of customers. Well, maybe compensate them with oil changes, a pre loaded debit card etc, but fixing the vehicle... It's not going to happen.
I may have to start firing off emails or make calls too about this just to have it logged. If anything it'll maybe push them to build a real hybrid qx60 come the second generation and not just make a qx60 mild hybrid again.