Regarding CNS, i don't know for sure and can't claim to whether it is a dillutionary instrument.
It is as you said, it's just a way to net buys and sells and make the net result that would hit the market smoother and have to send less orders to affect the market upon settlement.
But isnt the problem here that you should only net positions like this because you assume a company's stock float and a finite supy is a thing?
I think CNS assumes a finite supply and is why the DTCC just made a central repo where everyone can extract value via CNS.
If the market is truly about infinite liquidity and doing anything you want as long as your balance sheet allows you to, doesn't CNS act as an additional value dillution feature in all of this?
It's hard to get my point across on this. I hope you'll try and understand the point I'm trying to make.