Compatibility with people, at the astrological level, is not just based on one's sign or element domain.
It is necessary to see the whole synastry between people. You can also find people with multitasking abilities, predominance of the earth element, and not getting along, or other problems.
There's an entire branch of astrology called "synastry" that explores compatibility between people for any kind of relationship from friendship to romance to sex to business to co-working, family etc.
Sun sign astrology tells you very little about a person.