Major versions isn't a useless consistent concept because it's the strategy all browser developers use to determine when major features are added (vs bug/security fixes). Which is what Baseline is for, feature adoption.

So if Safari is adding a slew of major features once per year, and Firefox 6x per year, it doesn't matter. We have a baseline of what features as developers we can now implement without worrying about which browser version supports this or that. We see the baseline, we add the feature.

Last two major versions has been utilized (unofficially) by most people through Browserlist. It's been both suitable and productive.