adding heat protection?

[Andy Bettencourt]

There you go again, pulling that word out of your...anterior.

POOMA, babe. - GA

You aren't looking far enough into the words, you are getting hung up on that singular word.

The exhaust system is made up of an 'assembly' of components with an identifiable primary function per the GCR. That primary function is defined as

A passive system, whose components serve to convey the exhaust of an engine past the driver and away from the car

A heat shield attached to the chassis simply does not do that. I submit it's primary function is to shield the chassis (or another specific component) from any heat that the 'exhaust system' produces while it is doing its job.

I also submit we are at the agree to disagree point.