Currently, I'd view the Shimano SD-5 as the best available sandals.
They aren't as stiff as they should be, but I wouldn't call them actually floppy. I find them OK for medium length rides, but break out the old SD-66 sandals for longer rides, especially if it's going to be hilly and I'd spend a fair while standing.
Recent Exustars (SS502 onwards) are what I call "shoes with holes in" , with 3 wide-ish straps with neoprene filling much of the inter-strap gaps. I'd consequently expect them to soak up more water and stay wet/sweaty for considerably longer.