I wouldn't immediately consider the hotel metasearch products a problem for booking. It shifts traffic to different paid channels with different tradeoffs (eg. less fine grained control of spend if it's a revshare model). I ran the product development in marketing for a little while. Some years ago (ie. late in the game, largely due to politics), we started investing in cross channel attribution models to better direct spending.

Disclosure: I no longer work for Booking, though. I do work for Google, but am in NO way involved in Ads or travel and an not trying to comment on the company's business.