Pretty interesting topic, been reading for a while and only really want to add one thing (two things) that hasn't been said here, yet. It was said kinda indirectly, but with different meaning and focused on a different point.
Practicing "snap aim" intentionally improves reading and is a good way for practicing it. (Small Edit here to make one thing more clear: What I want to say is that it works both ways, your point is, that practicing reading will naturally result in snappier and sharper aim, that is correct, but properly practicing snap aim also vice versa results in improved reading, as it's tied together)
The logic is simple, you're trying to make a stop and go motion, stopping on every object, the focus is on the object, you don't just want to stop anywhere. To do that, you actually end up directly looking at each object individually. Especially in the pattern example you gave above (12345..), you'd treat and aim it as a bunch of tiny jumps, stop and go from circle center to circle center, looking at each of them individually as you have to click them (properly reading them).
When I practiced it, it felt only natural to watch the target+cursor in order to snap. Reading was necessary to snap aim, so in the end, the advice both improved my reading and my mechanical skill at aiming, as I trained my hand muscles in a new way.
With that said, I don't think it's bad advice, but when given, people should add a little more context and explanation as to what to think about / focus on when practicing snap aim. (I also practiced it on AR8, slowly moving up in difficulty, before going back to playing AR9 & 10, I even improved quite a lot at 10.3 from practicing reading on AR8)
And tbh, I want to make one more point here that is tied to this. Longer story, based on my own experiences as a player. Reading isn't simply learned as you go, you can imo go wrong and stuck easily, and this happens, when you play maps above your level / too high ar / complexity too early, before building the proper reading fundamentals.
I call this the "lazy eye" or "lazy reading", where you do not look at objects individually and mostly stare in the general direction at best. I've had this and also personally beat this habit and actually only like 2 months ago. I'm not a new player at all, but I've played DT and hard maps from the very beginning back in 2011. When I returned in 2017 I made an effort to improve sightreading and followed advice such as not retrying and nomod and saw lots of improvement, but my bad reading and bad consistency was kinda set in stone and whenever I tried individually looking at things, it felt straining and not really possible to keep up at all, I questioned it and wondered how others could do that. Naturally I just needed to practice it more on easier/slower maps, where my eyes would actually have had a chance to keep up and slowly learn and improve, but I wasn't given that advice and didn't think about it at the time.
Fast forward to 2019, I returned once more and again tried improving reading, but ran into the same issue, until I was actually given the advice to play AR8 and snap aim. That conversation that day fundamentally changed my reading and I finally started taking the correct steps to actually learn "real" reading and beat my years old habit of "lazy reading". For me it's now finally a steady process of improving my ability of being able to follow objects with my eyes faster and to be able to filter noise properly and look directly at objects in the middle/behind other objects and staying more focused, maintaining concentration all the way, something I could never do before. Object density would seriously mess with me, and when it passes a certain complexity, it still does, but that's natural, but I'm finally improving at it.
I really hope that fellow DT players / newbies that played too hard maps too early, that suffer from this same issue, end up reading this, so they can also fix their bad reading. It really helped a lot. My primary motivation for posting on these forums atm is basically just to share and give back. I've improved so much from advice I received, so I want to help spread what I learned.