I probably have a bit of a bias. I used my thief for things like Big Bomb and Guivre etc. before cap increase (free TH4, not because it was necessary to have an evasion tank, before people wah at me) and being able to take Big Bomb's Berserk, Evasion boost from Guivre, etc. along with with a large deal of alternative niche things in party/alliance situations seemed far more desirable than an abysmal increase in damage once every seven and a half minutes (ten if you are full meriting Feint).
If you're insistent that Assassin's Charge is actually doing something for your parse (it isn't, trust me), then go ahead and full merit it. One is all you
really need in Aura Steal, but I personally see it as far more useful (and definitely more fun

).