(“nominally negative but not apt to spark someone’s ire”)                                     
You know that old line that proper mothers used to preach to us: “If you can’t say something nice, don’t say anything at all?” Heeding that advice when asked about the techniques of fellow professionals is a good way to maintain the slender threads of civility which tie our ego-driven equestrian community together.

For the most part a neutral answer is relatively safe. “Well, it works for him…” is nominally negative but not apt to spark someone’s ire. Is that failing to stand up for your principles? Not precisely, but if someone asks you (as a professional) to evaluate a colleague’s work, to whom do you owe the truth? A close confidante—surely. A valued long-time student—hopefully. But not everyone. It isn’t so much (in Colonel Jessup’s words) that they “can’t handle the truth.” More that they might share it with someone who cannot.

Rather than a flat out evisceration of the individual, some general observations can do the trick assuming that the listener is smart enough to connect the dots.
A few examples:

Making your horse more adjustable is certainly an important goal. However, keeping the big picture in mind you have to intermingle loosening and suppling him behind saddle or you impair the gaits.

Generally speaking, when a horse is anticipating, punishing him is not a viable solution. It just makes it worse. I would go back and deprogram him, extinguishing his misconception with other exercises.

I am not a fan of drilling the same thing over and over, even more so if the horse is having trouble. If you can pinpoint the root cause of the problem and choose exercises to solve that, you can go back to the primary exercise and find more success.

There is a line in the old FEI rulebook which cautions that Submission does not imply “truckling subservience.” That is worth thinking about.

This way I avoid the confrontation which arises if I tell someone they are wrong. Better to simply point out alternative ways to help your horse understand without him becoming a victim of unintended consequences.