Yes, because per FreeBlock there are 3 entities(ArmorStand, Shulker, FallingSand). Additionally the FallingSand is teleported every tick.
But I don’t think this will cause any noticable lag.
Does the gravity tag affect fallingBlocks?
I don’t know.
The falling sand really doesn’t need to be teleported, it doesn’t fall when assigned to the ArmorStand as passenger. The real reason for the teleporting of falling sand is to prevent it transforming into a real block when it is aligned on normal block level. It is teleported to y=-1. The “is a block under me, then turn into block”-logic happens at -1, where no block can be under the falling sand.
Edit: But ok, I could optimize the plugin to only teleport FreeBlocks that are aligned with the normal blocks and a block is under it.
As well, you can open an issue on github to ask for a Key to prevent FallingSand from turning into block or you can add a Mixin in your code to do it your self :3