Correct, BUT, back when endorsers were generally respected, talented, and lauded, their endorsement meant something. Today, an endorser can flout their endorsement of a brand as a badge of honor. In effect, their endorsement is a validation. This can be perceived as an "approval" or endorsement of them by the brand.
I understand that and see your point. However most of the "world class" drummers have achieved their validation through much more concrete means than whatever association they may have with the company that makes their equipment. Either they are famous from their own talent or the fact they are in a successful group or employed by a successful artist or whatever. I'm sure Steve Gadd doesn't think his fame and reputation is linked to his Yamaha endorsement deal. Perhaps some small portion of it actually is from the ads he appears in or the clinics that Yamaha sponsors but for the most part he is a famous drummer because of his abilities and that is the reason Yamaha wants him as an endorser (as would most any other drum maker). I don't think you'd ever hear him start a conversation with "You know... I have an endorsement deal with Yamaha" (or even less likely "I'm endorsed by Yamaha").
Every bigger company likely has a roster that includes many drummers you've never heard of. Sort of the farm team of folks who either have some modicum of fame or show potential to perhaps become more well known. Even these folks usually have some degree of talent or notoriety that got them the deal and usually are not bragging about their endorsement deal.
In my experience it's the nobodies you encounter that will say things like that. I've met my share of them through the years and no one who ever brings that up is a "somebody". It's always "yeah. I have an endorsement from GKS Drums*" and it's never quite right as it is always "I'm endorsed by them" and not "I endorse their drums". More often than not it will be a young guy who only plays in local bars (if he even gigs at all) that bought into the endorsement sales scam that I outlined above. They received a totally meaningless "endorsement" deal in return for buying a set of drums. This little bit of ego stroke sealed the deal. They bought a set of "custom" drums just for the bragging rights of being able to say that one sentence and having their picture and maybe their bio appear on a website somewhere along with every other customer the company is similarly endorsed by. As I see it anyone who says stuff like that isn't worthy of my interest. I mean I'll politely listen but that's as far as it goes. I guess if it makes them feel good or their friends and parents then that's fine. They may be in for a rude awakening when they go to sell their endorser set and find it's worth about a quarter of the "wholesale deal" they thought they were getting.
If you haven't yet read Bermuda's article that bpaluzzi linked above you should check it out.
* Generic Keller Shell Drum Co.