I like Matteo have flown many kites and I can agree that there is undeniably an advantage to faster kites. Not faster as in turning ,though that can be great for some things, but faster as in actual speed through the air.
Yes smaller kites go faster, but thicker smaller kites are slower than thinner smaller kites, the viron comes to mind. Maybe thick and thin are misnomers. The correct term would be low and high drag kites, to which the thickness of the airfoil is a large contributor. There are to me many examples of this but the principle is quite simple and that is the fatter something is the more resistance or drag it will have. Now it is not always as simple as that because some shapes can vary greatly how much drag they will produce and is why sometimes a foil kite can be much thicker than the tube on an inflatable. I would think though where the shape is similar then thinner is always faster. So for inflatables with tubes then thinner is always faster. You only have to look at thin carbon supported kites to see how fast they can go or the new high pressure thin tube kites.
We are not discussing cell count, but larger kites and light wind particularly benefit greatly from reduced drag. Increased cell count may or may not reduce drag, drag is not always as simple as that, things are 3D and not 2D. Weight does increase with cell count and that is an issue.