Nothing cleanses Contagion. It's design philosophy is similar to that of the vampire skill line where you get a crappy debuff in return for something useful.
I think that the other effect, Malady, can be cleansed so Mara's balm should work as a decent defense against that if you're not playing a Templar.
The problem with Malady is that every stack of it counts as its own debuff.
So if you want to cleanse all 35 stacks you would need to use 7 Extended Rituals in a row.
A full cleanse like Maras or Wyrd Tree is probably your best option.
Ye pretty much, same/similar issue with relequen. With how stupidly easy it is to apply negative effects these days (especially through status effects, which is its own balance problem), sets like relequen and jerall shouldn't be straight hard counters vs classes like templar. The only proper counterplay that exists is cleansing revival in the blue CP tree but if you play nocp you essentially have no counterplay vs jerall or relequen unless you wanna waste an entire 5 piece to do so.
Jerall should've a way bigger curse on the person using it tbh.