“I meant the “I’ll Be Missing You” song, not Every Breath You take.”
Got ya.
“But for the Police, you are wrong, guitarist Summers wrote songs too. “
Maybe a few, not many though.
As for whether a guitarist gets credit for adding riffs or whatnot to a song, it’s not standard practice, but every band decides for themselves.
It's about equal. On Regatta, Copeland wrote more, but on Synchronicity they both wrote one, but Summers cowrote another one. All the others it's equal, plus there were B sides. They won a Grammy for a song Summers wrote, but the only Grammy for a song Copeland wrote was a written by all three.