Andrew, I would say that you have "made do" rather well.
Once you get more time in on using the Z6, I will be interested to hear how you relate to Nikon's new mirrorless ILC cameras in comparision to the Olympus OMD mirrorless cameras that you have been using for quite some time now. (And TIA.)
Had another day out with the Z6 and the 24-70/4S. I'm 99% positive that the 24-70/2.8G f-mount lens can go away, as can the D750. For what I use it for, the Z6 can handle it. I have a couple more tests I want to run the Z6 through before I get over that 1% hurdle.
Now, compared to the likes of the OMD EM1.1 or EM1.2:
The EM1.1 and 1.2 have a lot more "extras" like ProCapture(similar to the "precapture features on the Nikon 1 series) and what not. The Z6 is a lot more lean in that department. Where I had major issues with the EM1.1 and EM1.2 were the C-AF functionality. For some ungodly reason, Olympus decided that they would give you group area AF options much like Nikon's group or D9/D25....well sort of. The options description in the Olympus manual would lead you to believe that the C-AF would function that way. In truth, what it does it give you a larger cluster of AF points, but it does not allow you to control which AF point in the cluster is the main AF point and then use the other AF points in the cluster to support that. Oh, no...Olympus decided that the cluster would automagically pick which one it thought was what you wanted. For sports, it would often focus on the feet or in cases of hockey or lacrosse it would focus on the stick. If you are shooting at f/8, not such a big deal. It becomes a big deal when you need to shoot at f/2.8 because of the poor lighting conditions.
The EVF on the Olympus EM1.2 is very good, but the Nikon is even better. Bigger, less lag and smearing.
Size wise, they are very close, and I'd say the feel is a wash between the 2.
Olympus put the power switch on their OMD cameras on the left, while Nikon still has it around the shutter button, which I much prefer.
I don't think I need to mention either that the larger sensor on the Nikon just gives you that much more headroom for post processing. Usually not that big a deal, but when you need that extra dynamic range or you want to push the shadows...no contest, Nikon.
I'm honestly very, very impressed that Nikon got this much right in the first attempt. If better is the trajectory for the next Z camera, and I have no reason to believe otherwise at this point...Nikon is going to be a force to be reckoned with in the mirrorless market.