That's a pretty big assumption.

I like to say that network hash rate specifies the maximum possible level of security, but as the hash rate becomes more concentrated the actual level declines from the maximum.

I haven't thought through your valuation metric itself.

It is somewhat a tradition on this forum (especially in the Bitcoin section) that people make up their own metrics and post the results, generally in the form of graphs. Sometimes these are viewed as useful and are followed for years, sometimes they fall flat and are quickly forgotten. You might want to try that.