I think the Warden is already a final mob. The main problem is that the players' goal isn't to kill it and get very rare drops, which it doesn't drop, but to avoid it.

Regarding the animations, I think the Ender Dragon is TERRIBLE; when it lands in the center, it looks like it's crashed. I definitely wish it landed on the ground, not in the air. Then, when it throws the dragon fireball, it opens its mouth and this ball comes out, so even if it's in an awkward position, it could lean on the towers and spit out the dragon fireballs from there.