I don't think that they jumped the shark... take the recent ep wherein Negan and Fr Gabriel both covered themselves with walker insides to try to survive the multitude of zombies around them. Gabriel got sick, Negan did not. It just seems like a Russian roulette situation to me, meaning it's possibly fatal, possibly not. That's why they only use this tactic when things get really dire, like when the walkers overtook Alexandria.

This doesn't seem to apply very neatly to Mr. Nick on "Fear the Walking Dead," however, who used to put walker blood on his skin repeatedly.

They have done this numerious times and the times during the fights. IT NEVER HAPPEN BEFORE!!!!!!!!!!!!!!!!!

SPOILER BELOW.

I might've missed some of these moments you're referring to. But take Tobin, for example; he suffered a deep stabbing in the chest with a blade coated with said grue. It should be treated like a bite by a walker.

The writers always just do whatever is convenient to them at that moment. That's also why characters are quite stupid a lot of the time and zombies can sneak up on people whenever the script needs it.