Now you are moving the goalposts. The request was for evidence of a slow natural process for arch formation, and I provided that. Do you accept that evidence?
The relatively rapid erosion of existing arches is a different question. Is that rate constant or is it accelerated by human activities? This also seems to imply there were many more arches in the not-too-distant past, which is reasonable since evidence of collapsed arches in Arches NP is pretty easy to find. (And another very nice place to visit!)
From Batten’s article:
The conditions that formed these arches do not prevail today, so no new arches are forming in the National Park. Again, this is consistent with the real history of the world from the Bible, with the arches forming under the special conditions that prevailed in the Flood or soon after.
Also, I have been unable to find any support for this claim:
Forty-three collapsed between 1970 and 2015.
(I did look.)