Jonathan Morrison from TLD has been a long time Final Cut Pro X evangelist, which is one of the reasons why I've always liked the guy. For a while I sensed that people thought of Final Cut Pro users as amateurs, and the push was to switch to Adobe Premiere Pro. Fortunately, the tide seems to be changing, and it's largely being spearheaded by Morrison and his TLD cohorts. Even YouTube star Marques Brownlee recently made the switch over to Final Cut Pro X after testing it out.
Why is Final Cut Pro X so good? A lot of it has to do with optimization and speed. Not only do I find it much faster to use on my MacBook Pro when compared to Premiere Pro, but when it comes to video export times, it's simply no contest. Even the underpowered Intel Core M 12" MacBook from 2015 can handle 4K exports just fine, as demonstrated in Morrison's video.
The bottom line is that Final Cut Pro X is generally the best NLE for Mac users. One could argue that for end-to-end productivity, Premiere Pro has an advantage due to Audition and After Effects, but I think that even that's debatable.
That's not to say that Premiere Pro isn't good, or that it doesn't have any advantages. It's just that, for the average workflow with an average Mac, Final Cut Pro X provides a smoother and more consistent experience with less crashes and much faster rendering, exports, etc. That's largely been my experience when comparing the two.