It's not. Especially at f/1.4.
1. For those unfamiliar with the term, focus peaking is a feature of most mirrorless cameras that highlights areas of the image that are in focus, usually in bright red. It makes it very intuitive to adjust the focus precisely, so much so that you soon find yourself subconsciously making fine adjustments by leaning slightly forward or back, rather than manipulating the lens.
> This is assuming your subject is relatively static or at least cooperative.
Well, there you go, that's a pretty important caveat. It makes e.g. candid photography pretty challenging.
I see it as being similar to an innovation token in software development. Choose to learn one new thing at a time, not two or three.
https://mcfunley.com/choose-boring-technology
Once you're comfortable with a 50mm with autofocus, go nuts! Turn off AF on your lens or body. Practice with manual focusing.
Buy an old Canon FD lens and see how delightful these vintages lenses are on a modern body! Then, attach it to a Canon AE-1 and learn how to shoot black and white film!
Lots to learn; just don't bite off too much at one time.
In my opinion, focus peaking is somewhat useful for video, macro and astro. I say somewhat because it depends on the implementation. Some implementations (e.g. Sony) also apply in-camera picture settings (which adds sharpening to the output of the JPEG engine - which feeds the EVF), which can give you a false sense of sharp-focus. You'll see a ton of red, when actually the red is coming from the JPEG sharpening, not the change in focus.
Can you put forth an example of a real world situation that we can discuss?
For me, photography is not about being an expert camera operator, its about efficiency, and how productive I can be to create an image that I have visualized in my head. I care more about the final result than the process. Personally, I am welcoming the new AI/ML based focusing systems which can be trained to automatically put the focusing point on the subject. I don't think I can ever go back to the optical view finder and dslrs.
Cameras these days have over 700 focus points, and some high-end ones have thousands.
When you stop down, more of the frame is in focus - and focus peaking will tell you something is in focus, when it will not be in focus at your desired aperture.
One way to check if your camera behaves this way is to make the aperture smaller and smaller - does the live display darken significantly? If not, then your camera is not adjusting the aperture until you take the shot.
Of course, if using a fully manual lens, this is not an issue.
A Canon 50mm f/1.8 at f/8 as as sharp as anything you'll ever use -- outperforming many professional lenses.
In the long run, though, a prime helps you to understand what goes into composing a great image. It takes time to learn a focal length and learn which focal lengths resonate with you.
I have recently dabbled with a standard zoom for the first time in ages -- to me, it is now a collection of f/4 prime lenses that are accessible with the turn of a dial, each of whom have their own perspective, character, habits, and temperament. As I work to compose an image with it, I now decide, before I bring the camera to my eye, which focal length I want and select it. If the composition is off, then I move to bring the image together. Without extensive experience with primes, I'd never have understood the power of the changes in perspective that even small changes in focal-length can bring. (See a sibling comment of mine on this post waxing poetic about the differences between 50mm, 40mm, and 35mm.)
(you can, of course, get the same experience at lower cost with discipline and duct-tape holding a zoom at fixed focal lengths for days at a time, but most people don't succeed with that approach)