Note that things you draw within a single Graphics object are
batched, but multiple graphics objects are not batched together
are the rectangles uniform?
because you can draw one, generate a texture, then create a bunch of sprites (one-per-rect)
if the sprites share a texture they will be batched
http://pixijs.download/v4.1.1/docs/PIXI.WebGLRenderer.html#generateTexture
if you have many different shapes you can draw them to a canvas,
use the canvas as a texture "spritesheet" and then make all the sprites you need
and since they all share 1 base texture (the canvas) it will batch
advice from chad in gitter: