Coinbase makes money in a down market because of trading volumes.

I guarantee you coinbase stock is going to be highly correlated to the price of Bitcoin.

I would disagree. Coinbase's value is based on volume and volatility. If anything, stable values are the worst time for exchanges, as experienced in early 2019.

Ehh, sort of. Volume is highly correlated with return due to the wealth affect. When crypto crashes people stop trading.

For a normal exchange yes, but for a Bitcoin exchange the long term revenue is going to depend on future interest in Bitcoin which is highly correlated to current price