Liandry's Torment is an awful design because of how it breaks DOTeffects.

Because Liandry's exists, Riot cannot create a champion with long lasting magic damage dots, since this item just means you just burn somebody for an absurd amount of damage.

The existence of this item makes it so the majority of Riot's "DOT" abilities can't be actual "DOT" effects, and are usually either just multi-hit nukes (Taliyah, Ornn, Yuumi) or spammable magic damage nukes (Azir, Sol).

The last time they added a DOT ability into the game was in 2017, when they reworked Maokai's E to have a DOT component.

The last time a magic damage DOT was added into the game on a new champion was in 2012 when they released Nautilus.

If you want to know what happens when a long duration DOT is allowed to exist in League, look no further than the "Accept Death" Morde build.