Many studies have been done, showing that decay is reliable. While the specifics are beyond my understanding, you can even look at decay rates in old supernovas to show that even in the distant past, decay rates have not changed. This article discusses it about have way down:
https://www.astronomynotes.com/solfluf/s4.htm
So , while you are free to doubt the reliability of radiometric dating, the studies you quoted on variable rates only confirm that it is valid within its known limitations, with minor variations in decay being negligible.