Jiren is stronger than a God of Destruction. This is somewhat open to conception, but he is definitely stronger than Belmod (Universe 11’s GoD).
Toppo, who is a candidate, hasn’t fully mastered the powers of a God of Destruction, and therefore he must have some sort of weakness that an experienced God of Destruction doesn’t have.
Additionally, since Toppo is a new God of Destruction, he wouldn’t be able to counter an Ultra Instinct user (without using Ultra Instinct himself), nor would he be able to tap into that type of power. Meanwhile, Jiren is able to dispatch an Ultra Instinct user without much hassle.
Jiren is able to defeat Belmod, the current U11 God of Destruction. Meanwhile, Toppo is a candidate, who is still training to become as strong as a God of Destruction. His current power only represents that of a GoD in training, nothing close to a real God of Destruction’s power. Meanwhile, Jiren is able to defeat a real GoD.