You should start with that framing because that's actually a valid point that's worth considering. Although I think you only really want an incompetent at the helm when you could otherwise off him if you're expecting a long drawn out conflict. As soon as killing him becomes a way to destabilize things and you're in a position to capitalize on it then it makes sense to strike.

Iran not being in a position to capitalize on Netanyahu's demise lends credence to your stance that killing him right now is at best a wash for them.