If you think the extra 50 skill points is not worth playing a single mastery, then why exactly would you want to play a single-mastery class? People have already proven many times that you can make pretty much anything work (and work well) as long as you have a solid skill synergy to use as the basis for your build, and single mastery-classes are no exception.
For obvious reasons single mastery-classes need to try harder to reach acceptable stat thresholds, but the game already gives you so many other sources of stats besides just gear and masteries - not to mention gear alone can easily make up for the stat loss of having one less mastery bar. Not sure why you’d think otherwise if you’ve actually seen end-game gear.
In the end, it’s all worth it if the synergy your build is built on is strong enough.
I think it’s stupid to make a single-mastery build just to sink your extra 50 skill points in the mastery bar. Essentially what’s happening there is that you’re devoting 50 extra points to stats with zero of the gains from actually having a second mastery - and unfortunately for you, the devs like to distribute the game’s strongest skills between different masteries. Because balance.
Single-mastery builds make up for the stat loss with stronger core skills and better synergy, because the thing about each individual mastery is that many of its skills share a common theme. The trick is to find a setup that works, a combination of skills that makes picking a second mastery unnecessary.
While these builds actually got an indirect buff when the devs decided to incorporate stat gains into mastery skills - many mastery skills now also offer extra (secondary) stats, resistances and other survivability boosts - thanks to the current itemization trends, dual-mastery builds will always have the upper hand in terms of pure offense or defense.
In exchange single-mastery builds are potentially more versatile (solo Occultist has a ton of innate resistances, which makes it a lot easier to meet resistance thresholds) or just better at doing a particular thing (the Demolitionist build in the forums specializes in lob effect skills aka targeted AoE spammage).
A single mastery build with just extra stats instead of skills… that’s just dualclass lite.