Even with a cost of 4 AP you probably can misuse it to solo fights. Glass-cannon, Lonewolf, all those give me some AP skills, deal tons of burst damage, go into sneaking, wait until all cooldowns are down, deal again ton of burst damage and go back into hiding, rince and repeat.
Really. So even though the 4 AP cost for Sneak is already so prohibitive as to be basically unusable, in your mind it's still too powerful and needs to be nerfed or removed.
To be blunt, I do not care at all, in any way, if anyone chooses to abuse Sneak to solo fights, making them take 5 times longer. That's tedious and not fun, but if someone wants to sabotage their own experience like that, they should feel free to do so. There are a billion ways to cheese the system in this game, its not feasible to stomp out each and every single one.
I do care that Sneak is not useful for non-cheesers who are probably the majority of players.