Unfortunately I need true thunderbolt as I'm using the Apple thunderbolt 3 => 2 adaptor to connect to the thunderbolt => firewire adaptor to connect to a firewire audio interface! (hopefully I'll upgrade said interface to the thunderbolt 3 version this year). I have looked into the docking stations and did in fact buy (and return) the very impressive Caldigit T3. My only issue with these devices is the huge heavy power bricks they ship with.
My requirements are a bit niche as it's to go into a flight case for an onstage setup so size / weight is paramount.
Reading this interesting article
https://www.akitio.com/blog/articles/60w-power-delivery-macbook-pro if the devices have their own power supply (which mine does) 60 watt is sufficient to power the (87w) laptop on it's own. It wouldn't charge as quick but crucially it wouldn't discharge.
That USB-C dock you mention is exactly the size product I wish existed, I can't see any reason why it couldn't be made.
I've given up on my search, I don't think such a product exists unfortunately. I will settle for running 2 cables to my mac, 1 for power, 1 for the firewire device.