Let's break it down and go for the obvious first.
The end of the barrel can be flat faced without any harm to the accuracy of the gun. How could the face have anything to do with the flight of the pellet, anyway? But... any future bumping of that flat face may result in damage to the bore edge. That just might affect the accuracy of the gun. I personally like BOTH a raised outer face perimeter with a faint bevel to the edge of the tip OD to take away the sharp edge.
The end of the bore (where the ID meets the face) should be crowned. I like a 60 degree bevel at the interface of the face and the bore. However, if properly done (on a lathe), I see no reason why 50 or 75 or 90 would not work. As long as it is symmetrical and smooth there should be no downside to one angle over another. I expect that any good crown job will be very accurately made (again, on a lathe) with a crowning bit... a good burr check... and finally a good polishing with a lapping bit and compound.
I am convinced that none of the above really matters as long as the transition from rifled bore to crowned angle to face is smooth, symmetrical and without burr or dragger.
Rule of thumb: If the pellet does not touch it as it exits the barrel, then it is not important.
Some of the best shooting guns I have shot have factory crowns that are not too pretty to look at. Inversely, some of the barrels with absolutely gorgeous and accurately made crowns just will not group like the others. So why is that? The problem is not the crown. It is something else.
Does the gun NEED a different pellet? Odd how our guns like certain pellets, yet another of the same model may need a different one entirely. The answer is that there are numerous variations of the bore (diameter, straightness, any choking going on?)... variation of the lands and grooves of the rifling (the highly regarded Lothar Walther match barrels for our guns have more lands and grooves, but their crowns are actually quite plain AND ALL LOOK THE SAME)... variations of the leade of one barrel to the next and how well they seat (or distort?) the pellet on average, etc.
Some people put an awful lot of importance to the crown. I look at it as one of those things that if done accurately just eliminates the crown of a gun as a variable in our quest for the "nail driver" accuracy we all want. Put another way: In my humble opinion, a bad crown can negatively affect accuracy (by physical interference and/or being non-symmetrical). But if it is not doing that... then it is a neutral that is having no negative OR positive affect. One good crown job is no better or worse than any other good crown job. A crown is either problematic or it is sufficient. I say barrel crowns do not fit the "mojo" category.
Have fun shooting!