On a Fanuc resonator, the cut quality will be better on newer resonators. They have made a lot of improvements over the years to the beam quality and stability resulting in smoother cuts on the most recent resonators. On the machine builder side (at least LVD as that’s my experience), improvements have also been made to get better cut quality (new application features, new parameters, better beam delivery system, higher speeds, ...).
That being said, you can still get a good cut on an old and well maintained machine.
I cannot comment for other resonator manufacturers or machine builders, but I would assume similar improvements have been made over the years.