I've heard pros call Osisko horribly overvalued, yes.

You wanna buy shares in Osisko right now? No, I know, you don't want to buy shares in Osisko right now. Thus, it's overvalued. QED.

If Osisko's got the highest valuation by in situ, then it shouldn't be used as a comparison for a GNH share price target calculation. Could GNH become an uber-Osisko? Hey, maybe. But setting your price target based on that will leave you open for a huge disappointment if it doesn't happen. Don't play lottery with your money, play safe.