Every healthy meta has strong picks. The league does not ban strong. It bans options that take the other player's decisions away, because that is what kills a competitive mode.
Cheese = no counterplay
The test is simple: when this beats you, could you have done something different? If the honest answer is no, it is probably cheese. If the answer is "yes, I should have played it differently," it is just strong.
The usual suspects
Across titles, the same families get restricted: one-button lethality that ignores positioning, recoil-free lasers that erase the skill gap at range, and movement or equipment exploits that break the map. The specific items change. The pattern does not.
If it wins without a read, it loses the room.
Why the league draws the line
A competitive mode is only fun if outplaying someone is possible. Restrictions exist to protect that, not to nerf your favorite gun. Build around skill expression and you will rarely be on the wrong side of a ban.