Wow! A bold title, yet lacking a clear definition of what you believe Monte Carlo truly is. It appears overly simplistic and misleading in its characterization of Monte Carlo and its applications in forecasting.

Firstly, could you explain why a P/E ratio can't be used in a Monte Carlo simulation?

Valuation models typically require the estimation of future cash flows, discount rates, and other relevant factors. Each of these components may be influenced by various random variables. Introducing uncertainty through forecasting these variables can impact the reliability of the valuation model. Despite the approach—whether it's absolute valuation or relative value—valuation models inherently seek to minimize something. The residual, what's left over, describes the randomness in what is being forecasted, and this randomness evolves over time.

The valuation methodology you are proposing seems to ignore how this randomness evolves, whereas Monte Carlo attempts to describe the evolution of this randomness. Monte Carlo is a robust method; you might benefit from exploring a couple of books on the topic.