Your also forgetting cloak has 2 morphs, Dark Cloak removes several overtime effects and Shadow Cloak increases your critical by 100% for your next attack, so even if someone is a vampire and even if mistform made u invisible they would still use dark cloak at least to remove any negative effects from them such as lingering fire damage which can kill them in seconds if they don't react.
It's more of an issue with any class except NB's to get around IC and all the NPC's. You go down in the sewers as a vampire and get owned by all the fire from the NPC's but, have no way to de-aggro easily.
Invisibility may make NPCs stop pursuing/attacking you but if they have no other players nearby to target once you go invis they will begin going after you again once the invisibility wears off, which means it technically isn't a de-aggro but a delay or reroute to someone else, the latter of which could easily be used to lure on someone and get them killed if they're caught off guard.
Guildmaster of Power With Numbers in PS4 NA Server's Aldmeri Dominion.
Proud Founder of the Yaysay cult! DOWN WITH THE NAYSAY CULT!! #ToxicRemedy