The absence of an attack surface is as small as an attack surface gets.
Yes and the things that these chips process used to be processed on the main CPU, relying on software to prevent malicious access.
Now the attack surface, which used to be every implementation of every software, is reduced to the implementation of the world separation these chips provide.
You still aren't talking about the technology, you are spouting "common sense" nonsense like new chips using single digit watts of power are less efficient than old chips using dozens of watts of power.
Garbage.
Edit: again, what is the cutoff? Should they still support procs from 1995? 1990?