"Unskilled Player" category kind of assumes the person doing the reporting can accurately judge what good skill is. This is a very false assumption.
I would love it if Riot had an automated response program to the "unskilled player" report. If you reported a player for unskilled, it would respond by giving YOU feedback:
"We reviewed your report, but since you never upgraded your trinket or bought a single ward, we have determined that your jungler is actually highly-skilled, and we are demoting you to Bronze 7 instead"
"We reviewed your report, but we have determined that Nasus did the smart thing by split-pushing. If you had just defended your base, Nasus would have won the game for you, but you decided to chase Ahri through an unwarded jungle."
"We reviewed your report, and we have determined that a Janna with only three kills is not unskilled. She also had 47 assists. Perhaps you shouldn't have turret dove Annie eleven times."