Apples Paste has to have a long life span, this is why they use what they use.
this is generally the case with all Manufacturers of Computers/Gpu's etc..
it's neither poor nor great, it's an "ok" Paste.
a better performing, more fluid Paste should be replaced every couple Years, thats the Reason.
A Kryonaut will perform a lot better, more performance (less throttling), less noise, lower temps, probably longer battery.
So there's a lot to gain, but also a lot to loose because of the high price tag of the machine.
the 16" cooling is decent, if you don't have Problems i would not risk the warranty.