Solus is actually going to the 1st Shard to check up on how Minfilia is doing. While this isn't obvious in the English version of the Black Rose plant conversation, it's much more obvious in other languages, especially the German version. That version also makes it sound like the increasing light on the Source has nothing to do with what the WoL is doing and everything to do with there being a Flood of Light on the 1st Shard.

So if anything... I'd say hat Hydaelyn's plan for stopping the Flood of Light on the 1st is going to go wrong not because she messed up, but probably because Solus is going to mess it up for her. At the moment, no one knows that Solus is back and is going around doing Ascian shenanigans. So he's an Out of Context Problem for Hydaelyn and the WoL. And Minfilia being Minfilia and Hydaelyn being Hydaleyn, they both go back to the WoL for help.