Leverage helps of course but I don't think it's unreasonable to expect someone asking for a raise to know whether or not they're asking for a reasonable number. If market rate for a given position is $150-200k TC and you ask for $300k not only are you going to get told no (quickly) but it's going to make you look really bad.

I've gotten 10-15% raises before without a competing offer or any other leverage simply because I could show that I was a certain "percentage of market rate" when I was hired, but the market rate had increased ~teen% since then. So it wasn't as much me asking for raise, it was me asking to have my compensation keep pace with the market/inflation.