This is something I've gone back and forth on over and over, and I'm going to apologize in advance because it'll probably end up really long ... also it's not all directed at the original post, more of a general rant about the whole "don't give up on your breed just so you can win in agility" thing.
First off, it's not a matter of "love the dog or the sport." I love my individual dogs, absolutely. I like most of the Goldens and Labs I've gotten to know. I also like most of the Border Collies I've gotten to know. If I'd grown up with Border Collies, I probably would think they were the best dogs in the world. Does growing up with Goldens and Labs mean that I just have to never do as well in agility as I could because getting a Border Collie would mean I love the sport more than my dogs? Rehoming my current dogs or getting a BC puppy and ignoring them would be awful, but when the time comes (in several years) to get a new dog, it'll probably be a Border Collie. And that says absolutely NOTHING about my love for the dogs I have now.
I don't think it's really possible to judge until you've had the experience of competing at high levels of agility with a Golden (or similar breed), putting several years of effort into improving your dog's speed SO much, training as well as you possibly can, and STILL not doing as well as a bunch of very mediocre trainers/handlers with Border Collies. Every time Dusty and I had the best run of our career thus far, I would think maybe this is the time that all our hard work will be reflected by the placements, and almost every time there was some Border Collie ahead of us, or someone would mention how lucky I was that all the Border Collies were over at the USDAA trial because otherwise we wouldn't have placed. We never got within 5 seconds or so of the Border Collies. By the time Boo came along I knew a LOT about how to train agility, and he has pretty much the best obstacle performances he could possibly have. Still not enough. He's faster than Dusty, near the top of the "other" breeds instead of somewhere in the middle, but he would never make finals at Nationals or place in a decent-sized 20" class. There's nothing I could have done with these dogs to achieve the level of success that someone with a Border Collie can achieve even with bad handling and mediocre training.
Don't get me wrong, I LOVE everything about my dogs and wouldn't trade them for anything. But it'd be nice to have some actual recognition for all the work I put into them. People who saw Dusty when we first started competing know how much he improved, people who see Boo might say "whoa, that's a nice Lab," but there are many more people who say I should get a Border Collie because I have the skills to do really well. I'm a pretty competitive person, I'm used to doing my best in everything I do and getting some tangible reward for it. Obviously I appreciate the intangible reward of seeing our improvement and knowing that my dog and I are working as well as we can, but it's not fun to see the dog I think is the best in the world down toward the bottom of the page. And it would be even worse to keep having Goldens who are better and better, but see them farther and farther down on the page as the sport becomes more dominated by BCs.
That said, I hate seeing people who actually just aren't very good trainers or handlers getting a Border Collie because they think it'll solve all their problems. Then they end up having the exact same problems with the BC. It's not fair to the dog, because the handler thinks the dog should be magically good at agility and then gets mad when the dog doesn't meet their expectations. Or people who are new to agility (and any serious dog training) who get a BC because they're "good agility dogs," but they don't know anything about basic socialization and how to meet a high-energy dog's needs, so the dog ends up aggressive or develops really weird obsessive behaviors.
And I do know several Goldens and Labs who do really super-well in agility (like the Flashpaws goldens, my friend's Lab, and Quiz if Stephanie would ever focus on agility with him!
: ). I would LOVE the opportunity to have a Flashpaws golden, and I'm always looking for breeders who consistently produce Labs or Goldens with that much potential in agility. But if that opportunity never arrives, I still want to succeed.