Just a theoretical question about bore lasers

It seems there are basically two categories of boresight lasers:

• extremely expensive ones that are pretty accurate
• more affordable ones that get bad reviews for their accuracy.

it seems like all of them use a smaller laser reticle than the chamber bore. this means that the laser itself needs to be made pretty damn accurately; it needs to chamber properly so that it's seated concentrically, and the laser needs to aim true and straight through the bore. If it isn't, you don't get a good reflection of where the bore is really pointing. This means you need a purpose built device that's well machined, and with a precisely seated laser that's qa'd for accuracy out the metal device.

Thing is, nothing is more accurate than the bore right? The laser could actually be truer or less true than the bore, but nothing will match the bore accuracy as well as the bore itself. So if all I'm trying to do is rough sight in some sights and scopes, and I don't intend on dry firing at all, what would be wrong with using any laser I could find that emits a light pattern that's actually a hair larger than the bore ? It doesn't necessarily have to chamber, and by filling the bore the bore itself would be the "aim" of the laser, meaning the "accuracy" of the laser doesn't matter; there is no "accuracy" in fact, it's just filling the bore with a bright, straight light. With no requirement for chambering the laser either I can use the same laser in every caliber.

Wondering what y'all think about that from a theoretical point of view. I know that finding a laser that emits that large a dot yet could somehow be angled into the chamber to emit down the bore would be a challenge.