The amount of struts on a kite won't impact it's water relaunching capabilities in lighter winds
The shape/profile of the kite, more specifically the leading edge shape/profile is what will influence this the most.
In less than 15 knots, the simple fact that your kite gets wet (or worse Wet AND Sandy) adds a
considerable amount of weight to it, which pretty much makes any kite with fewer struts as heavy or Heavier than a 5 strut kite that is DRY!
Furthermore, your ability to relaunch any kite in light winds and deep water depends on various other factors like the current and the actual wind speed and wind density at the surface of the water, which can be very different from one light wind day to the next!
On some light wind days you'll have very little difference between the wind speed 25 meters up and the wind speed at the surface of water. On Other light wind days, you can have HALF or even Less than Half the wind speed at the surface of water and significantly more wind higher up. The image below is a perfect example of this. That day, the wind was practically non-existent at the surface (3 knots or less) and up where the kite is, a steady and dense 7 to 9 knots breeze.

In winds closer to 10-12 knots or less, the main focus should be to keep the kite DRY and try your best to avoid dropping it in the water altogether.
I said it before but I'll say it again, in low winds Flying Skills is the most important factor, then using longer, thinner lines comes next.
When foiling in winds below 15 knots, using standard lines thickness and length makes practically no sense to me
Fewer struts kites are an asset for foiling in general, but definitely NOT a necessity. I regularly use this 5 struts - 12m kite you see above in winds of less than 10 knots for foiling.
Foil kites will collapse and invert more easily in light winds, so not always a great option UNLESS you are a HIGHLY skilled foil kite pilot, and there aren't many of those around.
Christian