Those papers are basically repeating the folklore, but in a more formal setting. Consider the phrase
A right angle in a trace can cause more radiation
“Can” means “there is a possibility of”. No number specified.
“more” is unqualified. 1% more is more.
So it could mean “there is a 1% chance of 1% more radiation”, in engineering terms it is useless. The paper then goes on to explain
The capacitance increases in the region of the corner, and the characteristic impedance changes. This impedance change causes reflections
Those are plausible reasons, but without any numbers, pretty useless. The paper then dives into recommendations
Avoid right-angle bends in a trace and try to route them at least with two 45° corners.
Oh, so no EMC test report from anechoic chamber in controlled conditions, for a range of different frequencies?
If I gave that to my boss, he would just toss it back and say “get me some numbers”.
There guides are usually written by FAEs, who are often good engineers, but ultimately are just repeating stuff they have heard others say. Without some numbers, I really wouldn’t trust them any more than the guy on youtube.