Weird hill to climb, but it is definitely obscure enough to be unpopular ;)
I would argue that "best" is always subjective, so there's no point in any discussion beyond that.
However, that's no fun, so let's play along. I don't disagree with you, but I don't agree either.
Milk as a chaser for foods is nothing new. Where it fails is as a palate cleanser. While it definitely will cut through most foods, it leaves its own taste behind, and coats the tongue by virtue of its own residue and saliva mixing.
That means that once you've taken that first sip, you don't always get a full taste of anything eaten after that. Obviously, some foods will cut through the milk, but they have to, which changes the experience. That change in experience can be enjoyable, depending on exactly what the food is and what kind of experience you prefer.
As an example, hamburgers often have acidic condiments, produce a lot of fats in each bite (or should), and have lot of texture. So, with milk as a beverage, your between bite swig is going to be a reliable counter to the condiments lingering in the saliva and dulling future bites. Conversely, the textures of the meat easily clear the milk residue in your mouth as it delivers its own. So each bite and sip combo enhances the next.
That interplay may not be something every diner wants. They may prefer that the acidic components stay between bites. They may want the fatty unctuousness of a greasy burger to remain uncut by the fats of milk. But, it is definitely going to be a different and pronounced difference from water, sodas (where sweetness is similarly going to change how the burger is experienced) or things like iced tea.
Now, Doritos live and die by their coating. A plain tortilla chip is a flat, but pleasant experience. So what you dip them in is the real flavor you'll get. Those flavor powders are designed to tickle all your flavor sensing taste buds at once, and intensely.
Milk is definitely strong enough to counter them. But, the flavor delivery system that is a Dorito lacks the ability to completely cut through the milk with a single chip. It takes multiple. This can be good or bad by preference, but it definitely changes how flavors are presented as you consume. The first chip after milk is going to be heavily subdued, and it will mix with the milk residue. It won't be until the second or third that you get the full flavor back.
Again, preferences differ. But milk does mean that the experience of Doritos is more subdued. To have each chip deliver its full taste bomb each time, you need a palate cleanser that wipes most of the flavor powder's residue while not leaving much of its own, or has one that's complementary.
I think that's why you enjoy Doritos and milk. The milk complements the umami fairly well, while providing a good wipe of the spices involved. You'll end up with multiple cycles of tastes, which prevents the brain from getting fatigued by non stop intense flavors.
Now me, I prefer the experience with a fairly equal preference between water, iced tea, or a low hops beer. That's where Doritos hit best on my palate.
But, a hamburger with milk? Hell yeah. Same with sloppy joes. Spaghetti would be a hell no with milk unless the sauce is really bad.
Milk gets underappreciated as a food adjacent beverage. It isn't just for cookies and pb&js.
