How much weaker are T1 really, having lost Zeus?
Doran is a good player but he has a history of choking when it matters no?
Problem is not that Doran is bad, contrary to popular belief, he is extremely good. But he ain't no Zeus who is a top 3 player in the world. Also Doran is a tank top and Zeus is a hypercarry. So the problem they came across was that they had no hypercarries in the team with Doran being a tank specialist and Guma being an util adc. Smash is a hypercarry specialist, hence they brought him in and kid shows promise. He absolutely killed Ruler in his second game with the team.
Zeus forced Keria and Guma to play weak side cause he's a hyper carry and needed tons of resources, and bringing in Doran (who usually plays weak side) allows bot and Oner to cook up shit. With Doran on the team Oner can play carry junglers and Guma can start getting resources. Also Doran kind of fathered Zeus domestically in LCK, but is known for being an international choker.
However all of the above might be cope from T1 fans, as most of them called +Doran -Zeus a sidegrade. so only time will tell