I have to point out, if they were 100% reliable, why change out any of the springs or buffers?
There's plenty of examples of DI rifles going 50,000 rounds with little to NO cleaning, and they only get parts like extractors replaced. Why aren't they considered reliable? They are being shot without modifications or alterations.
If someone chooses to add another piston to a design that already had one, that's their business. I find it difficult to accept they couldn't have spent the money and bought a better grade DI gun. I do know for a fact DI guns work fine in competition and on the battlefield, and can be equally reliable.
In reality, guns are chosen as tools, defined by the task at hand. Caliber, barrel length, optics mounting, and furniture are more important than choosing to move the piston from one end to the other. If none of the first meet the need, piston location can't make up the difference. If anything, the amount of time someone can dedicate to effective practice, along with affordable logistics to support it, has a lot more to do with success.
It's not the gun, it's the shooter. Good shooters win matches, which type gun they used is almost irrelevant. They can even make using a AK seem easy. A poor shooter can't even qualify with a $2,500 gun. Worry about moving the piston when skill level is so finely tuned the operating characteristic is what is understood to be an answer.