No, the Bills best outside receiver had less yards than Palmer. The Chargers best receiver had 300 more yards than the Bills best WR and their #2 guy was only 100 yard short of the Bills best. So the Chargers had a better WR group than the Bills.
To talk about Johnston like that is lame. When he was drafted he was not considered a polished ready pro, but a guy with desirable traits to develop. His yards jumped a good bit (nearly double) in year 2 while having almost twice as many TDs than any Bills WR. If Johnston did not show the year 2 improvement, Palmer would have had better stats and the Chargers would have probably tried to keep him.