Let me start off with a straw man: static scene autofocus with mirrorless cameras is more accurate and more consistent than with DSLRs.
That indeed has been my experience with virtually all the mirrorless cameras (versus almost all the DSLRs). Even though some older mirrorless cameras may be a bit sluggish to get to the focus point (e.g. the X-T100), getting accurate and consistent focus on landscape, still life, basic travel scenes, and posed subjects is something that every one of the mirrorless cameras achieve quite well these days.
Where autofocus is still a contentious subject is with action.
And here's the reason why: most photographers struggle with keeping reasonable and steady framing on fast and erratic action; they have no extra brain cells or ability to also control and direct an autofocus system at the same time when they're struggling with maintaining their composition. They tend towards "all automatic" focus modes for action.
Remember, even the best of the mirrorless cameras are not showing the "live moment" in the viewfinder as in the DSLR: mirrorless viewfinders are always lagged. In some cameras, such as the Sony A1/A9 and Nikon Z9, that lag is minimal enough so as to be ignorable, plus the viewfinder never blacks out. It's easy to follow action.
In other cameras, that display lag and blackout can be significant and problematic, so when you start trying to shoot bursts on fast moving and erratic subjects your ability to keep the camera composed and focus sensors consistent on objects in the scene becomes quite troublesome. Most people already have the problem of maintaining composition on erratic action, even on DSLRs. Thus, compounding the problem with a lagged and blacked-out mirrorless display just makes everything break down faster.
That's why Sony's upcoming real-time tracking changes and real-time Eye AF for animals are so desirable (particularly on the A1). In effect, Sony is trying to promise you that you can keep your brain centered on composition and the camera will magically work out the focus. As opposed to Nikon's absolutely terrible and completely wrong-headed 3D tracking system on the Z6 and Z7, where the user is expected to be fiddling with buttons to establish cursor positioning before it will try to do anything magical (and then, the magic itself turns out to be a bit disappointing). Fortunately, Nikon fixed that with the Z9, and now the Z9 is right at the top of heap in terms of real-time tracking.
I've been struggling with trying to describe how it is that I'm getting rock solid results for very tough action sequences with my Z6 and Z7 while others aren't. What it boils down to is attention to details and practice.
Simple question: did I prefocus, did I let the camera find the mountain lion and focus, or did I do something else? Answer: all of the above.
The details come in learning what the system does and doesn't do. In what settings you can make prior to shooting that might help. In understanding what the camera is actually doing. In eradicating things the camera is doing that get in its (and your) way. In using the right lenses (yes, the newest AF-P lenses tend to do a tiny bit better than the oldest AF-S lenses on the Z cameras, for example).
The practice comes in just working (and sometimes experimenting) until you get good and consistent results. For me, that's been tens of thousands of images on the Z's.
Thing is, getting good autofocused results on erratic and fast action is possible on most modern mirrorless cameras (and DSLRs). However, not everyone is willing to take the time to understand the details of their camera, let alone practice enough to get the best possible results consistently.
The casual shooter that's only using their camera once a month or less simply wants magic.
We've moved closer to true focus magic over the years, but it's still not completely there yet, even though Nikon seems to promise it with the Z9. Meanwhile, a lot of commentators and reviewers aren't spending enough time with every camera that comes down the pike to really say that they've done the detail and practice work. It doesn't help that the camera makers are closed lip about what the camera is actually doing and offer little help.
For example, when Nikon launched the Z7 with great fanfare, not a single Nikon product manager or employee I talked to could describe what the autofocus system was actually doing (they still can't, by the way, and I still have at least three unanswered questions that only a Nikon design engineer is likely to be able to answer). Every Nikon Ambassador I encountered in those first demonstrations was using AF-S (single servo focus) because they weren't getting the knowledge (or time) to master the continuous autofocus system. So when you hand cameras to people who've never seen or used it before, what do you think happens?
Sony and Fujifilm, bless their souls, have a longish history of iteration now with their mirrorless focus systems. A lot of people don't remember just how bad the original Fujifilm or Sony autofocus was for continuous shooting. Far worse than where Nikon was with the original Z6 and Z7. But Sony is up to firmware 5.x software for the A9, and technically we're nearing about a dozen focus system updates across the Alpha line. Likewise, Fujifilm is at least a half dozen significant iterations in their focus mechanics. Nikon, to date, is probably three iterations in (the Z9 is a big leap fourth).
Even with all that iteration, I'm still not sure we're at the point where anyone can truly claim "just pay attention to the framing and the camera will do the rest." Though with the A1 and Z9 we're getting close.
And thus autofocus remains a highly contentious subject.
It's time for another straw man: with almost no exception, I'd rather have the current top-end mirrorless autofocus system from any vendor rather than any autofocus system I was shooting with 12 years ago.
Put another way: we're far better off than we were not too long ago. And every camera maker is working frantically at pushing things even further into the good.
Stop arguing and do more study and shooting. Amazingly, the autofocus system you're complaining about will get better when you do. /mic drop
