I don't think some angle to the string is cause of tendinitis. If you know how to play in a relaxed you can test several different angles and some wrist bent as well as a straight wrist, and it won't cause any problem. Most common cause of problem when trying to obtain an angle is when you force a wrist "fixation" to keep it in a straight position in order to reach the string angle, but you also can do it in a relaxed way without that wrist fixation and it won't cause any harm.
About the sound result, I agree Segovia was probably the best, but I don't know if it is really only a matter of the "perpendicular positioning" of RH. I think the angle choice also has a lot to do with your personal characteristics of finger tips and nail. If your nail is hard, regular and simetrical, a perependicular position is great, but if you have some irregularities on your nail, then more angle may help to fix the "problem". Although Segovia used the knucles almos in line with the strings, we can clearly see on his videos that he attacks with some slight angle, it is not really perfectly perpendicular, and he uses a lot some side-attack with a small "slip" of the finger over the string to obtain a rounder tone. Check out this video at youtube, which is one with the best image and sound quality I've found with Segovia at his best level, here playing Llobet:
On this same youtube user you will also find another high quality video on Torroba with a lot of close ups to his RH.
What I do agree is that most players with too much angle are those who search for a sweet tone but they stay there and they do not vary too much the tone color, which sometimes is quite boring.