I switched between the D750 w/ the 24-120 to a Z6 with the 24-70. Kept my 70-200 and got the adapter. Honestly, the main reason I switched was that I got tired of lugging the D750 around, especially while traveling, and I have had a bunch more video work coming my way lately. The Z6 is I think the best video dSLR/FF mirrorless out there right now and I save over a pound of weight. It's definitely more money, though.
You could also look into some of the smaller Sony mirrorless systems like the a6000 series. I don't have experience with those or the Fuji, but lots of people love them for lightweight mirrorless systems.
Edit: also something like the Sony Cybershot RX100 V might be a good option as well.
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