Is pressure of presta valve hard to read by design?
The problem is your pump's valve chuck. Some valve chucks press the valve's center pin, which lets the pressure from tire to pump and allows reading the pressure. Some other chucks, such as the one you have, do not do that feature. If pressure drops to near zero after every stroke, there may also a leak somewhere in your pump.

Replacement valve chucks are available, you can replace it if you do not want to buy an entire new pump.