How strong is an 18 DND?

Ability Scores and Modifiers A score of 10 or 11 is the normal human average, but Adventurers and many Monsters are a cut above average in most Abilities. A score of 18 is the highest that a person usually reaches. Adventurers can have scores as high as 20, and Monsters and divine beings can have scores as high as 30.

https://roll20.net/compendium/dnd5e/Ability%20Scores#:~:text=Ability%20Scores%20and%20Modifiers,-Each%20of%20a&text=A%20score%20of%2010%20or,scores%20as%20high%20as%2030.