[Dr. Acula]

Yes, it is normal for an un-bled master cylinder to lack braking pressure. Power brakes can very easily compress air bubbles inside the system. I'm guessing you have at least some pedal pressure with the engine off? Without the power assist, it is harder to compress the air.

You'll have to bleed a new MC too, so why not bleed the one you have on there already? If you get good braking, great. If not, you have practice for when you bleed the new one.

Brake fluid is (relatively) cheap.

(I'm assuming you got the used unit in good shape from a reputable source.)