True, but what encounter are you designing? If I'm allowing a powergamed character in there I plan for it. Intelligent and powerful creatures target them with just as many tricks up their sleeves. These powerful beings aren't alone, and their posse attacks the rest of the party. In my opinion, it is very doable. Though it might get boring always having a Kaiju fight while the rest of the party is doing normal party stuff. The games I have allowed powergaming, the powergamer has always been the first one bored with the campaign.