Booking travel these days is far more complex than it used to be. And car rentals are a great example. Using Hertz and Italy as an example, when you book through 1-800-HERTZ, hertz.com, or hertz.co.uk, you believe you are booking directly with the operator. But that's not true as your reservation is shifted to Hertz Italia. And as mentioned in a couple of posts, they are a totally separate entity that Hertz USA has no control over - and Hertz will tell you that. In addition, many of the Hertz pickup locations in Italy are actually franchisees - so you've added another layer to your booking (I'm starting to feel like six degrees of separation). So even when you think you're booking direct, you might not be booking direct.
Many of my car rental experiences have been in Italy where I found that my Hertz President’s Circle elite status - acquired through my USA rentals - meant nothing. I also discovered that many franchisees had a NO-ONE-WAY rental policy on specific models. These cars were their money-makers - with amenities like incorporated GPS - which allowed them to earn higher rental earnings per day. They did not want to give up those cars (to other franchises) so many created one-way restrictions. I learned - the hard way - for a one-way booking to always got the drop-off fee in advance, and in writing.
Thus, sometimes it's good to have an advocate (and better to have one with buying power/influence). Unfortunately, OTA's are not the best advocacy option. They are geared for one thing: SALES. They provide a low-cost option with limited support. SERVICE - and advocacy - are not their strengths. They just haven't built a staff for this because it earns them no revenue.
No one books an OTA for service - it's primarily about price and ease of booking. And this lack of a "service priority" became VERY apparent during March & April 2020 with multiple COVID cancellations. Just go read Expedia's reviews during this period. OTA's are great if everything goes "right" but if there's a "bump" you'll quickly find yourself working your issues out alone. Moreover, getting a refund or return from a disputed rental is far more difficult when working through an OTA. The car rep will say, "That's not our booking, call the OTA." And the OTA often says the opposite - if you can get them to answer the phone.
Hotels also have franchisee units or management companies operating them - even $1000+/NT 5-star luxury hotels - and far fewer issues than the car rental industry. For many reasons, the rental car industry seems to be more ambiguous than other franchisee and corporate travel options. Thus, buyer beware - Find an option you're comfortable with!