That's probably the #1 mistake made with this sort of thing -- over-tightening ruins washers/gaskets/o-rings, and as you discovered, causes parts to bind up.so much so that when I overtighten it it hard to turn the shower handle.
Are you certain about the seal at the bottom of the cartridge (purple gasket pictured in your post)? My first guess is that when you tightened it down you damaged it. The damage may be on the back side of the gasket, so pop it out (gently) and check the back.All the seals look okay - no corrosion (when I touch them they look/feel in excellent condition).
If every seal is really excellent, you may have cracked something in the cartridge, or there's a seal buried in there somewhere.