When we used to boil Amal carbs I uses a rolling boil
So you had both heat and movement
Now Amals have no plastic parts other than the float and it never seemed to hurt the floats and they did not soften or deform
I can see where he is coming from with the 200 F but I seriously doubt that the extra few degrees would make a difference
Most plastic parts are either Nylon or HDPE
From this
table you will see that nothing melts at a lower temperature than 100 C
The mould temperature is the lowest temperature that you can force the material to deform in a high pressure die casting machine
Welding temperatures are all above 200 C according to
this chart
Note I said a rolling boil not a visious bubbling boil
I also noticed he omitted rinsing the parts before drying
Even parts from the ultrasonic bath get rinsed , twice. first time in slightly acid or alkaline water then with brake cleaner
Which rinse depends upon what cleaner I am using
The one from RGS is acid so needs an alkaline rinse & most detergents are alkaline so need an acid ( 5% vinegar ) rinse .
When we boiled I found the dishwasher tablets with the ball in the middle worked best
Degreasing before you boil is always a good idea