I just wonder why Kasumi believes a shirt and pants are somehow less hot than a swimsuit. It should be the reverse.
Oooh! (puts on physics professor glasses)
Blah blah bah, another lecture about stuff everyone knows.
I know that wearing more clothes in hot regions can be cooler/prevent being burned alive (why else would people in the Middle East be wearing full body outfits and turbans). But in this context there is barely a case to be made. Those pants aren't going to do anything a bikini bottom won't do too. Or look at Sakurako's frilly bikini. It covers more and has the advantage of being air funnelling.
Kasumi's shirt being bright and thus not absorbing heat is fine, but a white bikini is nothing unusual. The only advantage of this shirt is that it gets so soaked with sweat that a breeze will cool her down easily (which will have her catch a cold real fast). Brilliant.