Between discovering Loki has been posing as Odin, fighting Hulk, and taking on the new threat in Hela, the third Thor solo film already has plenty going on without wondering how Doctor Strange is going to factor in to the story.
No matter the time gap between Doctor Strange and Ragnarok, the future Sorcerer Supreme is merely a beginner with magic when compared to Loki.
Somewhere in there fans will discover the changed circumstances Hiddleston references and sees Loki and Thor working together again and against Hela.
Strange doesn’t figure to be a major part of Ragnarok as there are many plot threads currently waiting to be sewn together.