market economics are like newtonian mechanics. It's all so wonderful and logical and even elegant, until the dimensions expand a few orders of magnitude, and then all the rules break. Having worked on a trading floor for 20 years I know how this works. Swamping a market with huge trades is definitely considered manipulation by essentially all authorities, and indeed is a form of monopoly power, which even economic theorists will agree is undesirable. Jane Street just got a mega fine for exactly this in India, btw.