do I really wait until early spring for ANY root work on ANY plant?
In all honesty, no. You don't have to wait till spring. I've repotted maples during the summer too...
The problem is that there are so many different species, varieties, sources, climate or age differences etc which cause difference in care.
Thats why people that have been doing this for a while will always ask for as much information as possible to give any advice or give the usual "it depends" answer.
I made a guess on Hinoki and was luckily corrected by more experienced members.
As you mentioned yourself there is quite a difference in repotting a Thuya vs Hinoki.
For new people in bonsai however I feel it makes it easier to start out with general guide lines like "repots are done in spring" or take "1/3 of the roots off".
Does this mean you can't repot trees other times of the year? Or cut off more? No, but you have to know what you are doing. Especially the aftercare.
You learn things like that by reading forums post here and actually experiencing it yourself.
For example by Walter Pall; repotting maples during the summer? Np apparently, as long as you know what you're doing.
So I've tried it this year (emergency repot) and the trees is now pushing a lot of new fresh growth.
A while ago I bought a little Chaenomeles, it came in a little nursery container so I was planning on repotting now.
However when I did some research here everyone said to repot after it flowered, but before the new leaves come out.
At the moment the leaves are already opening and the flower buds seem ready to unfold any day now. So after more research it seems I need to repot during the fall.
Repotting during the fall means different aftercare then during spring because of the coming winter.
For example, it will need a lot more protection against the freezing temperatures. Out of experience I know I won't be able to provide this, so I won't just blindly repot during the fall and see if I can find a solution by repotting it earlier.
Maybe not the best example, but just trying to say; give as much info as possible (and clear visible images) when asking for advice or research as much as you can.
If you're still unsure, just fall back to common sense....