Incredible indicator?
Well, not from my perpective. It "can" be a good tool, but like anything else it can be abused.
Let's talk about it. My biggest issue with it is that it is a "predictor" of future events and none of those are exceptionally reliable. No one (except Jesus) can predict the future and he ain't into stocks so he doesn't weigh in.
The P/E ratio is a critical component of the calculation of the PEG. The PEG can only begin to be accurate if the P/E is accurate. Plenty of things can make it inaccurate. Some are perfectly honest, some are NOT. Just like the rest of the market (and life too).
So why can the P/E be unreliable?
(redacted for brevity)