I thought the clamshell vents were associates with the Hessessey/Heffner exhausts that curve up to the same heights but with no insulation. I really don't don't know, I liked the look of the billet vents more so it wasn't even a question of "if I should change them."
It seems the warped vent issue is mostly a result of generating very high engine temps followed by immediate shutdown with no air flow. The polls seem to show no strong correlation between warped vents and type of exhaust system. As far as I can tell, the stock exhaust is fairly well insulated and dissipates heat over a large area. Regardless of type of exhaust, a hot run should be followed by a cool down. Failing that, open the clamshell until everything cools.