Of course it is possible to have an entirely inadequate lug for pure lugged construction without any butt brazing, and with a well mitered joint, it doesn't matter, as the lug has largely been made redundant, which is good practice, and I'm not advocating anything contrary to that. As I noted, you don't need miters with the right lugs, and clearly a half mm bikini lug is of questionable strength and not the right lug for that.

I don't want to speculate too much on inferior methods, but the wall thickness of the lug tubes are thick enough to be a butt on a cycle tube, presumably the miters are tight on the lugs and have good strength, and there's a large brass fillet to help reduce stress risers at the miter. The amount of steel-to-steel contact seems to be in the range of sufficient at any point along the joint. The concern of a stress riser where the laminated structure effectively thins due to a poor miter is conveniently reinforced by a large fillet. I hesitate to draw any conclusions, since of course, there is no good reason to risk trying to make an intentionally inferior joint.

I just wanted to point out that, in my opinion, the "truism" is more about making the lugs largely redundant and irrelevant when it comes to joint integrity (yet still useful as a reinforcement like a gusset and for holding tubes in place), but isn't really true as a general rule for lugged joints, otherwise we'd all have serious problems with our lugged BB shells and chainstays which have exactly zero tube-to-tube brazing.