probably not gonna rehash here what is debated on http://www.kiteforum.com/viewtopic.php?f=1&t=2397685
What you seem to miss here, is that the "floaters" we consider here in our context are still sinkers. They can still be sunk, angled correctly for waterstart, and considering they have the similar surface area as your sinkers and have at least the same ability to resist the pull of the kite. But with more thickness and something like 20-30l of volume, as opposed to 3l, they don't sink that fast, and not as deep, which helps between two power spikes in marginal winds.
Its way easier for me to practice balance on the alaia in a swimming pool than for example a corky surf board.
That's quite flawed, sure you're more balanced and stable, because you're chest deep in the water, whereas the corky surf board would keep you waist deep.
And in our context of foiling to get back on the plane, being deep in the water takes extra power to overcome.
I agree however, that when powered enough that getting on the foil is no problem, it is somehow easier to do some slow speed transitions and foot switches when the board is fully submerged.