Case by case in my estimation. There is just no way a blanket statement like that could ever prove true IMO but that doesn't mean one shouldn't give the dealership involved a try or chance.
If I purchased the vehicle there and keep all my services there, I do think or hope they'll take good care of me and I won't be bashful if needing to step up my game to get things resolved. Social media and report cards or service surveys are big ways of rewarding good customer care but it works the other way too.
In my case, I've found the dealers work out fine thus far. My default is based on a Mazda purchased new 3 years ago and a VW purchased new 2 years ago. In these cases, service and warranty issues will go " by the book " at the related dealership. I am a shopper so any out of pocket situations are those I tend to shop or price check but otherwise I'm pretty loyal.
My Mazda LOF is a plan that I purchased ahead to secure the LT o/c at a favorable cost so that ties me in so-to-speak plus, they cater to my schedule very well so it's working good.
The thing I like about keeping things within the dealer is straightforward service records/history and the leverage one has if things get dicey on a service problem or warranty coverage issues.
Service problems or issues with vehicles can get quite tangled with the customer that was at Hank's Lube Shack last year, the corner garage for an LOF 7 months ago and now is now at a dealership for an LOF when they discover a leak, or a stripped thread on the drain plug or some other issue. Tracking down who did what or getting resolution can be simplified by how you manage these things IMO.