or heavy work in the center of something, they are great - a little rough on the edges of things, but that can be avoided if the contact point can be kept in the middle of the plane. They are how I do all work on mild steel now (infill planes) if there's more than just a tiny bit, then filing and then check lapping at the end to confirm that the sole is flat and gets evenly marked by the lap.
Yes on the ability to mess things up lapping - I'd say things are likely lapped wrong more than right, but there's more information available now so it's not mandatory to mess things up. The very first plane I ever got was a "tuned and lapped" stanley 5. $85, cosmetically great. Toe and heel were more than a hundredth high -the guy who did the lapping just obliterated it trying to get every mark out of it that he possibly could've gotten out of it. would've been OK for jack work.
The issue that I'm not fond of with machining is cost, and then the follow-on to that is nothing is learned. It takes more time for most planes to be boxed and shipped than it does to lap. It's not reasonable for me to say that someone can get below a machinists spec on their first plane, but it's doable on the 10th. Then, the lap gets used elsewhere (flattening very bad irons, lapping other things that aren't even tools, and potentially even tuning miters freehand in a hurry).