Understanding valve seals

I'm in the process of replacing these on my mazda. They are metal caps that are POUNDED onto the tops of the valve guides and no amount of force with said cheap no leverage multiplication "valve seal pliers" would budge these bottle caps. I ended up using a modded screw type valve spring compressor to pull these off. After I snugged the jaws on the seals, it took 5 ft.lbs (!) break away to pull these off! 60 in/lbs on a 3/8 stud was almost 800 lbs pressure.