I'm not sure if I would disqualify trading volume because of leverage. From dumper perspective it does not matter if he fills 1000x buy offers form none leverage guys or 10x buy offers from 100x leverage guys. I need to think more about that.
it's important to remember, these are not real bitcoin markets. they are derivatives that settle to bitcoin. holding contracts at the wrong time can mean socialized losses. or the price can separate from the real spot market when leverage outweighs market depth.
13k BTC dumped on coinbase pro or bitstamp would definitely affect the price. i can't see coinbase pro's full order book but the shortened version shows only ~1500 BTC depth down to $7100 ($600 away), so imagine how far 13k would go.
We would see instant buy offers spam from arbitrage traders that would move price change to other exchanges like binance (with 2000BTC to 7100$ - only spot). There are also bunch of hidden offers that waits in arbitrage bots for trigger price. I think that 300$ -500$ price change is max that we might see from 13k BTC instant dump.
to an extent you are right, but you are also making
a whole lot of assumptions about supply and demand that we don't actually know. other exchanges might arbitrage down more than coinbase pro arbitraging up. it all depends on market conditions.