Your mistake: You say your friend's titanium cookset "doesn't seem to heat up as rapidly as my stainless steel set." No empirical data presented! And in fact, titanium has better heat transfer capability than stainless steel. Plus, it can be made thinner (although I do not know if MSR takes this step) because it's stronger, further enhancing heat transfer. And, the corrosion-resistant capability of titaniumbetter even than stainless steelensures that no crud attaches to the outside of the cookset, crud that can further affect heat transfer.
In short, titanium saves weight AND saves fuel. At least theoretically.In the real world, due to the thin metal in a cookset, titanium's heattransfer properties probably don't result in measurable differences when compared with stainless steel. So, no reason to buy titanium for that reason. But, as you correctly note, it is light, light, light.