No. K/D only proves survivability. Cacti generally get higher K/Ds than Peashooters, but their killing potential is actually the same or lower. It's the nature of the class, since they naturally stay away from most dangers.
I've played the Goat for 5+ hours and I have a K/D of 3.73. This doesn't prove anything. His killing potential is still slightly lower than most high tier zombie characters. You can get many kills, but you would have gotten more with other characters.
The Scientist's reload probably gets cancelled to avoid reloading while placing a heal station during ambushes. The Scientist needs to be penalized if he runs out of ammo while he's trying to attack you at close range, otherwise he would be too cheap. I think they should make an exception only for his heal beam.