^ horses with the right conformation FOR THEIR JOB will have a distinct advantage over those that are not built right FOR THEIR JOB. Of course there is the occasional horse that excels despite its conformation, but will it stay sound long-term? Unlikely.
This mare does not have a strong hind. She is too straight in the stifles and hocks to have the physical scope to jump or event at a high level. HOWEVER, that does not mean that she cannot excel in the lower levels. If she has the mind and the heart for it, she will be amazing - at the lower levels. I have never seen a horse that is this straight behind competing in high-level jumping and eventing. As much as the heart and mind have to do with performance, conformation does limit or encourage performance. It DOES depend on how a horse is built as to how they do in a specific discipline.
This mare does not have desirable conformation for a showjumper or eventer. That IS the bottom line. She might have all the heart in the world, but heart/spirit/whatever you want to call it can only make up for so much.
By the way, herring-gut is a serious fault, as it limits heart and lung room and therefore will limit stamina. THAT is the whole and sole reason why I would not buy this mare as an eventer or showjumper. I think I would have her in a heartbeat as a show hack, dressage horse, or trail horse, but anything that requires stamina will be harder for her than for a horse without the fault.
YES, racehorses often appear herring-gutted, to a degree, but rarely this much unless it IS a conformational fault.