If you have the time to dig out that old german book on razor manufacturing you'll see that the angle they considered correct was something around 17 degrees (you'll get the exact numbers if you put in the ratios from the book).
On the other hand you can't have too acute of an angle or you'll be out of business. Most famously Hartsteel didn't seem to have thought this point through and the first razors they sold had huge ratio of junk - you can read the feedback on the forums.

As far as old sheffield razors, if the spine of a razor is softer than the edge it is not possible to hone that razor to shaving. It's a simple geometrical issue. Actually, if you're really persistent and have nothing better to do you could make it into inverse razor i.e. the edge is where the spine is.
In any case I've honed old razors to where the spine + bevel flats had to end up making 2/3 to 3/4 of the width - with modern fast hones it doesn't take more than few hours. But that's certainly not how these razors were designed to be - for example I have ~200 year old razors that have bevel narrower than what Dovo and TI ships you today from the factory.


The thing is that whenever somebody starts telling me how tape or no tape is the proper way to hone I just learn that there's yet another novice who isn't good with neither hands on experience, nor making up theories that describe things correctly. As long as one does not abuse his razor maintaining it sharp removes so little steel both from the edge and from the spine, that the razor is perfectly good for hundreds and thousands of years. The best advise I have for these people is to learn to hone properly and stop abusing their razors. Then they'll be fine no matter what they choose to do tape-wise.