@craigmanning I think you misunderstand that ERG is not supposed to be a reproduction of road riding. It is a very specific set of programming that aims to hold a set power target.
The requirement is that the rider hold a generally steady input cadence so the controlling app and trainer will work together to achieve a power close to the target.
Hey in this is the fact that it requires steady input and no attempt to chase the power target. Doing so corrupts the process and leads to issue like you described.
You found have used the Snap and set it to Resistance or Standard mode. In those, the trainer acts more like your simple Kinetic Road Machine. If you push harder, the power will increase. Again, this is all about the modes and using that’s intended and ad you prefer.
With your focus on hitting +/-1w, it’s a hard goal, especially for a mid level trainer like the Snap. Other trainers may perform better, but the ERG mode is still something that may end with more variation than you prefer.
Based on all that, it seems you are best served with a standard trainer that you can control directly.