As has been said, combat is fluid, and formal stances are made in a world of classrooms and theory, not the reality of warfare, the streets, or your own home. What is a good stance here is not a good stance there, what is possible here may not be possible there. Especially in close quarters self defense, where situations are not clean cut, like they are in professional competition and classrooms. Are you going to attempt to take a shooting stance such as the isoceles against a robber with a knife a couple of feet away, or take a fighting position? Are you going to take a formal shooting stance if you are behind the counter of a gas station with someone threatening you on the other side? Do you even the time or space? Is it even appropriate?
I have great respect for competitive shooters, and the amazing talents they have, and the art they perfect. However, competition shooting has little bearing on real fights, save for situations where the shooter has the space and time to take set piece positions in ideal conditions. Remember its a SHOOTING sport, not a FIGHTING sport. The results these fine men and women show are amazing, but for many people and situations, beyond irrelevant.
Isoceles is a SHOOTING stance, not a FIGHTING stance. Locked in behind the gun, you are in the best shooting stance you can find. However, locked behind the gun with everything you have, you are extremely poorly balanced for anything and everything else. Its a poor stance to be physically attacked in, you are in the worst standing situation possible if someone tackles you, or tries to melee. You are strong as a shooter, and weak as a fighter. In self defense, its not always being able to shoot the attacker, you may have to fight with him, and a fighting stance is superior in close quarters civilian defensive situations, which often times do descend into scuffles.
Part of my view is extremely, extremely, way over the top old fashioned, and I'm still one of those who believe a bayonet is one of the best means of fighting point blank. But there is incredible truth to the point that at some ranges, a knife, sword, club, sap, blackjack, ect., can be more effective than a handgun, quicker, more natural. How many good peace officers have been shot with their own duty weapons after physical confrontation? The gun is not magical, does not mean you will win a knife fight. Its advantage of range can be quickly cut, and often times is, in close combat. In a standoff or running gun battle with criminals, the isoceles can be extremely useful in maximizing effective firepower; fighting a criminal at 2 feet might make the position worthless, or worse, dangerous.
You get a lot of people who will sit and say "isoceles is perfect for shooting" while leaving out "in perfect conditions" part of it. Remember that the laboratory is not always inclusive of all real life scenarios.