It sounds like you have 4 wheel power drums. In my experience, these should feel strong in moderate speed stops. Maybe not completely even L/R but should stop you pretty fast and easy from speeds of 30-50 MPH or a bit more.

This is not what you are seeing so something is not right. Suggest visual inspection of all 4 corners and bleed the brakes first. If you don't find anything wrong then consider booster or master problem.

If you want to stop from higher speeds well or repeated stops time to upgrade to front discs. If your system needs major work... especially the front, suggest you consider disc upgrade.