It certainly ought not be. That your rate resembles the market is a CONSEQUENCE, not a driver. The driver of your rate needs to be based upon the value of your services. Are you going to enable a company to make $500,000 more next year? Then if they want to pay you $50/hr because it's 'market rate', you need to tell them to kiss your ass.
The presumption is that everyone is already doing this, and that everyone has a reasonably correct understanding of what the actual value of their work is. This is a false presumption, but it is a presumption which is absolutely necessary for any defense of capitalism. Knowledge of value has to be spread equally or all of the promises of capitalism fall apart. Anyhow, if everyone DID know what the value of their work was and set their prices by that, the idea is that a market rate would establish itself, which certainly would happen. What we've got today however is employers telling everyone to set their rates by the 'market rate' and ignore any other drivers... which makes it very easy to drive down the price over time. That would be why the average salary of the lower 90% of the economy has only risen 1% in the past 30 years, even though worker productivity and corporate earnings have skyrocketed.
Cost-based prices are for gypsum and tile wax.
I know people who started out expecting, optimistically, to be able to charge (say) $120/hr, and who just a couple years later are shocked to discover that they're worth multiples of that.
Your rate is set by the market, not by your "reasonable" desired salary is.
In case you're wondering at this point: I think you should be charging more than this tool says you should. And, obviously, I don't think you should be billing people by the hour at all.