A certain individual isn't going to be considered beautiful by everyone. Each person is attracted to different things. So looks wise, no.. but there will always be someone who finds that person beautiful.
When it all comes down to it sure. It is true. People are naturally more comfortable with those who are on their level of physical attractiveness. While the more physical people are able to attract more possible candidates, in the end most people end up with someone within a few numbers of themselves (graded by attractiveness). If you are far less attractive, you might become self conscious, controlling, jealous. If you are far more attractive you may resent them/know you can do better, feel taken for granted, etc. If you got two 1s or two 5's or whatever together they can find each other beautiful and attractive and there's not going to be as much tension due to much difference.
I absolutely hate when people say that it is such bullsh*t and people only say it to make themselves feel better (ugly people say to feel attractive, attractive people say it to feel like nicer people/ never have had to worry about looks). I think very few people are beautiful, they are many attractive people and a lot of ugly/ unattractive people.