USB-C and dual input should not be required, you’d have USB-PD and so it goes to a USB-PD output charger, so in case of a dual port USB-C powerbank, it would have 2 ports, 1 used for input (and then 1 inactive) or 2 ports for output and when 1 port used it gets all power.
Recharging is about half to 2/3rd the Watts of discharging, example is Powercore II 2000 is 4A input and 6A output. That ratio is limited by Lithium cells.
Currently I’m as close to cable simplicity as possible, in that I don’t own lightning so I use MicroUSB cables and USB-C adapters but there’s inevitably going to be a loss of the adapter. I washed one once by accident.
Certain Anker powerbanks are incompatible with certain Anker products, example is the Powercore 10000 will not recharge the Soudbuds Lite, as the buds approach charged they drop their demand so low the 10000 turns off power (and it does the same with my Bose QC35) so I find carrying the Powercore+ Mini to recharge buds is required, so its carry the 10000 and the Mini for combined 13450mah with 2 output ports, pair with a Powerport4 to recharge them both with MicroUSB short cable and two longer USB-C cables and I find the cables dominate bulk still.