Although the OP describes his particular nightmare with actually trying to book travel, the most obvious reason to avoid OTAs is not booking, it’s when things go south. It’s hard enough to get a basic level of customer service from the airlines during disrupted travel, but if you’ve booked via an OTA you might as well head straight for the car rental lot. Should you ever venture on to TripAdvisor, you will see the most frequent and unhappy traveler complaints all start with “…and when I told the agent I had booked via XXX OTA, they said I needed to contact them directly as it was their problem”. Painful lesson, and one you need to remember.