I also had issues with cable tension on a similar bike, Z1 Luna. I finally tracked it down to the fact that the cable housing length and the few bends it has to reach the derailleur creates friction that makes it hard to dial in. This especially showed up in the middle of the cassette where cable tension starts to back off. I figured that wireless electronic shifting would alleviate the issue but didn't want to spend $$$$ for the Di2 or AXS systems. I decided on the Archer Components system that eliminates 95% of the cable housing and has a wireless pod shifter like the other more expensive systems.
I had switched to using cheaper steel cassettes and derailleurs in 11spd after the original 12spd. Sram GX stuff wore out and continued with them after installing the Archer setup. Initializing the Archer to the cassette was relatively easy due and shifting improved. However still had issues with cassette wear and switched to the 11spd Shimano Linkglide chain/cassette and now am experiencing nice crisp shifting. Still not cheap but the overall cost was half of the other available electronic systems.
I do suspect that the nm torque of the M620 is the culprit in wearing out the smaller cassette cogs though and time will tell if the Linkglide cassette, which is steel, will stand the test of time. However replacement cost is not bad at least.