To me a good RV Tech is one who has a good grasp of how things work and can apply that knowledge with hands on work.
A hydraulic system has very few parts, a storage system for oil, a pump to create pressure, a transportation system to send that energy to a point where a device can convert energy to work and then a return back to the storage supply point.
Almost every system in an RV is just like that, water in a tank, pump for power, water heater to do work and a drainage system to carry the left over or dirty water back. Electrical systems work the same way. Power on one side of a light and a return on the other side.
The hard part is not understanding that principle but in knowing how to apply that knowledge. Because the rate of change or advancement in technology is so great, it is in my opinion, impossible to keep up with everything a good tech needs to know.
Another thing a good tech needs to know is that he doesn't know everything but does know where to go to get the information he needs. That is why things come with manuals.
Good Techs are Jacks of All Trades, but most likely not the Master of but one or two.
Doug and Chris are really good probably great techs but admit they don't know everything and that they use manuals.