Has anyone tested to see if RoF removed a Protected cloak?
Yep.
Even Retrovirus can Plague it away.
On the other hand, Cloak nicely counters at least two cards - EQ and Poseidon
Not really. EarthQuake and Quicksand are both cheaper and will hit before you get to use your cloak. Try playing Seism and ask what he thinks of Cloak.
It also let's growth creatures get out of otyugh-omnomnom range.
But you could have instead used a Blessing or Chaos Power and been further ahead or just used Lightning, freeze or shockwave and killed/injured the Oty. And if your opponent isn't using CC himself those spells can be used to slow rush. Where cloak does nothing.
What does Cloak do to help you stop RoL/Hope, or any Rush deck?
What does Cloak do to help you against any AI?
Since Cloaks effect is not Yang and not infinite in term, it is ineffective. Between 2 identical Archetypes, assumedly it would be a fair division of games 50/50. Adding cloak to one does not increase its game winning potential against the other because the addition of the cloak reduces its offensive potential. The more I look at this card, the less I like it.