Re:

The biggest lesson I learned is that for optimal results, you should stick to your brand and find a sensor-lens combination that was designed and tested by the same company.

There is a strong inference here that the best results for a given camera make/lens combo would be from lenses designed by that camera maker and mount. We can adapt different maker lenses and bodies, but do so with adapters that introduce an additional factor that likely results in anomalies and aberrations, regardless of the published engineering general bench specs, even if they do not introduce more glass.

How many of us bother to focus calibrate our lens/body combos on an individual combo basis and tweak color spaces and curves within the camera? How much of an impact might these very detailed and time-consuming activities help?

Does shooting RAW and our chosen editors make a difference that needs to be addressed in processing?

Questions to ponder...