So a high P/E ratio, for example 80, would imply it would take 80 years to earn back the share price if earnings remained constant
That's not completely accurate - you don't need to "earn back" what you pay for the stock, since it's not a "sunk cost". When you buy a stock, you have an asset that you can sell at any time for fair market value. Your "profit" comes from the increase in share price plus any dividends (which lowers share price, but that's another topic).
If you buy an 80 P/E share for $80, it pays a $1 dividend (distributing all of its earnings), it's price is still $80 and you sell it, you still earned $1 in profit - you don't have to keep the share for 80 years to profit.
Also, stocks with a high P/E ratio often are expected to increase earnings significantly in the future. An 80 P/E stock would have a return on equity of only 1.25% (which is very low) if earnings were held constant. The market might expect low earnings for a little while, but is expecting earnings to rise in the future.
Yes a lower P/E is generally "better" all things being equal, since the stock has a lower price for the same amount of earnings per share, but a "good" P/E ratio varies between industries.
Value investors often look heavily at P/E to do initial screenings, but will not stop there - they will use other metrics and deeper analysis to determine why the P/E is so low.
Imagine seeing two seemingly identical cars on a lot, but one is priced 20% lower. Obviously you would not just assume that it's a great deal - you would want to understand why it's priced lower. Is there some hidden mechanical problem? Does the other car have some subtle feature that adds 20% to its value? The same goes for stocks - P/E ratio can identify "cheaper" stocks, but you must determine if it's cheaper because the market is undervaluing it, or if it's cheaper for some other fundamental reason.