To improve water pressure with this setup, I’ve tried changing the angle valve to one with less restriction (wider outlet visually). I think it improved but still not satisfying.

Will changing from flexible piping to rigid piping straight into the heater improve pressure or more recommended to install heater with built in pump?

Do newer heaters consume less electricity than old units like AC or no?

I have been told it is ~25 years old. However was only used a handful of times before 2021.