I didn't vote as I was too late but I would certainly argue that hogs are usable at level 4. Lvl4 hogs will wreck just about any th8 base and also weaker th9 bases. Having lvl4 hogs gives you a useable alternative to drags and gowipe for attacking near max th8 bases.
Personally I had lvl 4 hogs done before lvl5 heal and didnt regret it. Below is a video of me as a th8 3 starring a new th9 with lvl4 hogs (yes I had lvl 5 heal by then) just to prove they can be useful.
http://youtu.be/tyoawFjp5WA

