No... you should not have to stand on it to stop.

A few questions about the setup. Power or manual brakes? Original type or new master and what diameter?

In general some aftermarket calipers like the Cobra spec units I run and (I think) the SSBC pieces have smaller piston area vs OE. They need more line pressure for good stopping from either a smaller bore master or stronger booster or both. Weak vacuum to the booster or booster problems could cause this problem as well.