> How long would you say it takes your average, competent developer to become proficient in Rust?
I think it's exceedingly difficult to make such a broad generalization. There's a number of factors here at play, but for example, I think the struggles of a Rubyist learning Rust are very different than a C developer learning Rust, and are very different than someone who's proficient with both who is learning Rust.
It's also hard because there's also just other random factors. There's a semi-common experience where people try Rust, think it's too hard, quit, and then come back 3 or 6 months later, try again, and are completely unstuck. Sometimes it takes coming back two or three times. Do you count all of that dead time? Something in there helped, but it's unclear what, or why this affects some people.
Another theme of stories I've heard is a sort of Golidlocks situation about how "right" you think the compiler is. Some folks have the attitude that the compiler is to be seen, not heard, and should stop nagging them about things. Those folks tend to really struggle with Rust, even if they have lots of relevant experience previously. Likewise, some folks trust the compiler so completely that they will lose a bunch of time when a compiler suggestion leads them down the wrong path. Luckily, that problem is easier to fix than the former one, and is rarer and rarer every day. But these sorts of attributes are completely separate than what we think of when we talk "competency" of devs.
> In your experience, what's the best path to learn Rust in 2023?
This sounds tautological, but bear with me: it's whatever path gets you to learn Rust. That sounds trite but what I mean is that different people have different needs (see above) and so need different things. There is no one best way. For some people, the book works really, really well. For others, they either hate the writing style, or the pace, or just something ineffable. I wouldn't say that they're wrong for that, just that they'd be served by different strategies.
What I will say is that "I know other languages, I can just kinda start coding and pick it up" tends to not work for almost anyone. You either need to be quick to ask questions from the community, or be willing to do some reading, or you may run into some struggles that will take you longer to overcome than if you were willing to get some help. Folks who take advantage of community resources, broadly speaking, tend to do better than folks that think they can write some code and learn solely through errors, as Rust's semantics are just unique enough that some background and explanation can be extremely helpful.