There are multiple angles to the question. The first is defining what "good enough" looks like. Every person's definition of "good enough" can vary based on personal experience, personal expectations, and personal interests. My "good enough" might be a far higher standard than the next guy's "good enough". Another person's "good enough" might dramatically exceed my "good enough". Etc.
There are people who, without question, are "good enough" in their own mind and may even exceed the standard of "good enough" held by others even with inefficient techniques. In other words, with the appropriate practice and training you can do much better than most even if your technique is "wrong". To put it as bluntly as possible, no one has ever lost a gunfight because they were using the wrong stance.
...so to an extent those who hold it to be irrelevant are correct.
It's also true, however, that some techniques are more efficient than others. The modern iso stance and the correct grip on the gun provide the best level of control for running a handgun. Using the correct grip and stance you can deliver shots with more accuracy and with more speed, which is generally considered to be a universal good as it comes in handy during a competition or a gunfight.
If we were to take two versions of Dave Sevigny and program one to use Weaver and the other to use his existing technique, I don't doubt that the Weaver-programmed Sevigny would still probably easily destroy most modern iso shooters on any set of drills you could conceive of...but I doubt he could beat the modern iso version of Dave Sevigny.
If we're going to learn and if we're going to try and improve, it generally makes sense to get rid of any techniques that are inherently limited. Weaver suffered from a physical handicap that made his stance a necessity. If you aren't limited by that handicap it would probably be best to use the more efficient techniques. Simply adopting the new technique won't transform you into a rock star overnight...but it will help you break through personal plateaus if you're interested in doing so.