In fact Buz is repeating an old creationist strawman which anybody familiar with the EvC debate will know of. It is a classic PRATT that survives only because some people naively trust ignorant or dishonest creationist sources.
Index fossils are used for relative dating. However, contrary to the creationist falsehood it is first established that the fossil is suitable for use as an index fossil before it is used for dating. To put it simply, it is established that the fossil is common for a relatively short time period (in terms of geological dates !) and then not found at all. This can be shown by relative dating techniques, without need for radiometric dating. Once this has been reliably established the fossil may be used as a relative dating indicator. Contrary evidence, if discovered, may change that assessment.
Index fossils are used because they are a cheap and simple method of dating rocks.
This method is not circular, because the fossil is identified as a reliable date indicator before it is used.
As to Buz's latest, it's even worse.
The assumption of uniformitarianism by conventional science is a hugh factor so far as absolute dating goes with radiometric dating methodology.
Already a classic creationist strawman. Geologists accept catastrophic events when the evidence supports them. In fact there is no plausible mechanism for increasing radioactive decay rates by the amount required, let alone one that would work consistently for all the elements used in radiometric dating techniques. Nor is there any good evidence that radiometric decay rates have significantly varied.
The literal Genesis global floodist paradigm does not advocate for uniformitarianism. Since the Genesis account clearly depicts a canopy atmosphere before the flood, cosmic rays from the sun, etc would have affected the isotopes of all of the elements which conventionalists apply for dating the strata.
As usual Buz misrepresents the Bible. The "vapour canopy" is not "clearly depicted" in Genesis at all. It is an invention of modern Creationists. His science is even worse. Cosmic rays do not come from the sun at all. Even if the atmosphere was much thicker and intercepted more cosmic rays it would not drastically increase decay rates as Buz's argument requires - not for ANY of the isotopes used to date rocks, let alone all of them. Not to mention the fact that layers of rock are likely to prove rather effective shielding.
In other words this is ignorant bullshitting, and nothing more.
(Variations in cosmic ray influx DO affect carbon dating, but only because they affect the FORMATION of radiocarbon. However, a thicker atmosphere is not likely to affect that much, since it is in the atmosphere that Carbon 14 forms, when a cosmic ray hits a Nitrogen atom. Moreover, carbon dating is not used to date rocks and calibration with independent dating techniques allows scientists to compensate for that variation. So it's no help to Buz at all.)