In their mind they're purest, but they aren't. These are the same people who want to break out the QH into specialized versions of the breed (some developed for cutting, some for roping, some for racing, etc....) and adding new blood from outside the breed to improve certain traits (i.e. the appendix QH).
Don't get me wrong. I'm a huge fan to cross breeding and improving horses, but you can't call yourself a purest if you're wanting to change the breed into what it wasn't created as/for. Some breeders often do this within a breed by breeding only for the traits desired at the lose of other traits that often made for a better horse (but not for show).
The old foundation QH was a wonderful animal that you could ride all day doing a hard days work. It was a very versatile animal that did well at a variety of functions. You can still find them today. Yet many breeders are breeding for specialties vs keeping the great "all around" work horse that was the QH. Today you can find them bred for cutting, or barrel racing, or roping, etc..... because people want a horse that excels in the specific area more than the all around horse that is what was used when these competitions first started. It's all about having a horse that's better at one thing more so that good at all things.
Of course I'm just an old timer (even though I'm still under 60
) that remembered my QH that I got at 14 as a great horse for working cattle (the reason we had some QH) and riding long distances, hunting off of and racing my uncles truck to the curve in the road
. Back then when there was a competition it was done with the horses you worked with. Some were better then others at different things. There wasn't these big money shows and competitions for most of us. It was my working horse against your working horse for bragging rights
. None of those horse was going to win any of the big competitions they have today, but they could be depended on to so it all and do it all very, very well.