Lit venues do the price discovery. Their displayed quotes feed the nbbo, anchor the midpoint-peg used by dark venues, and give everyone a reference price.
This is why market-structure debates focus on the lit share of volume: dark trading free-rides on lit price formation, and if too much flow goes dark, the reference price gets noisier for everyone.
Example: a stock trades 40% off-exchange. The dark-pool and internalisation prints that make up that 40% are all priced from the lit bid and ask of the other 60%. Remove the lit orders and there is no midpoint left to cross at.
Related: exchange, dark-pool, off-exchange-trading, nbbo