Honestly, I don't see it as a massive issue.
I don't think the advantage it offers is that huge. Even without the extra cost, the loss of tempo is still real.
Not only that, across the entire spectrum of the format and the 900+ legal commanders, people are playing all sorts of things at all sorts of levels. Only a few of them offer any advantage over commander tax, but to me at least, it doesn't seem like a deciding factor when building a deck. I don't think anyone is building a deck to specifically save on commander tax, it's just a nice thing to have if you like the commander anyway.
In my experience at least, taxing someone out of their commander isn't a particularly effective or reliable strategy. It can be reasonably effective at times, but with all the fast mana, infinite combos and mega ramping available in the format, it's not often that it's super relevant.
In addition, most of the recent commanders that can skirt around the tax are ones that come from regular sets where the saving in cost is more relevant. From a design perspective, I'd assume it comes from a place of making them good in their "intended" formats (standard, modern etc.) and the relevance in Commander is smaller so they're happy to let it happen. Obviously, they know how popular commander is so they will always consider it when designing legends, but I'd assume that tax evasion is something they aren't too worried about because of how low impact it is.