What precision are you talking about? The super exact precise angle of xy° or something? That this angle changes if the blade has a belly does not bother you? And how does that "precision" show in real world use? Serious question.
A serious question deserves a serious answer. I'll give you my take. Most of the time, I use an Edgepro (EP) to thin the bevel behind the edge. I prefer a more acute edge bevel than most makers are willing to grind. And I'm fine with that.
I don't use a belt sander enough to thin the edge bevel and make it look professional. You, as a knifemaker, can probably do that freehand. I've tried, and I can't. Nor do I have the time to put in to learn that skill, assuming I would ever be capable of it. Thinning the edge on a stone takes a long time, and still looks bad when I do it. I can use the EP for a very professional looking bevel which I then generally freehand after that or put on a microbevel. Or both.
As for the bevel, if you want to keep it the same width over the entire cutting edge, you are correct the angle has to change. But I keep the angle consistent and the bevel widens at the belly and at the tip. Actually, the bevel has to change as the width of the blade changes. For my purposes, that works really well, and makes freehand sharpening very easy. A lot of people really dislike that look. I don't. I don't care much about the exact angle, as long as it's thin enough to suit my purposes.
As to your question about precision, for me, the precision in setting the bevel is paramount. However, if I'm looking for the sharpest edge possible, I've never seen a freehand edge that can rival one from my EP. And the beauty of it is, anyone with an EP (or similar system) can make that same claim. It's fast and repeatable. I don't do it that often anymore, but it is a very nice way to get my wife's kitchen knives sharp with minimal effort. I've also been able to get some younger people interested in knives and sharpening by showing them what a highly polished edge can do. Getting the younger generation interested in knives and sharpening is always a good thing, IMO.
I'll give you an analogy. I grew up in a golfing family. As a result of many thousands of hours of practice, I could easily drive a golf ball well over 350 yards consistently throughout my entire adult life. Many golfers can't do that. That's ok, we all have different abilities. I think it's easy, others think it's very difficult. I was lucky enough to have mentors teach me. Left to my own devices, I never would have understood what it takes to be able to do that. I was lucky.
Kind of like sharpening. I disagree that you can read about it, watch YouTube videos, and "get it". Maybe I'm just a slow learner. I've been told that before. It's (for me) a tactile feel that has to be developed, and while the EP taught me, it would have been faster to have an experienced person show me first hand. I would love to attend a session with Bob Dozier, Murray Carter or Phil Wilson, I'm sure I'd learn a ton more than just watching them on YouTube.