You are a thick one.
No, it is NOT listed as a root word. Look up above the photographic image I pasted in part to the Strong's portion for 4074 - Petros:
"Root Word (Etymology)
Apparently a primary word
See that? "Petros" is a primary word. It has 6 letters.
In the Thayer's lexicon section it is written as: Πέτρος
That's 6 letters: Pi (P), Epsilon (e), Tau (t), Rho (r), Omicron (o), Sigma (s). No letters were later added in that lexicon entry. It's defining "Petros," a primary word. And it defines "Petros" to include the meaning "rock . . unyielding, and so resembling a rock."
It is laughable that you -- a person whose Greek knowledge is so limited as not to be able even to understand root versus primary word, who can't count to 6 letters in a lexicon entry -- proclaim that these Bible scholars (who very likely have a good to superb knowledge of Greek) are just all wrong.
Right. Got it.
Now THIS is having the mind of Christ!!
Good show, mate!