TheVaultDweller
Front line cannon fodder
Well, if they do merge Supergirl into the Earth 1 continuity, that will certainly change things. As you mentioned, Supergirl actually has a rogues gallery that can provide a credible threat to the Flash, plus s2 of Supergirl is getting a full-on, more fleshed out Superman too (at least from what I have read). It's kind of crazy that it all started off with a very grounded-in-reality season 1 of Arrow.
And for all we know, not that much has changed. As Rip Hunter said, time wants to happen, especially really big, memorable events. And Barry becoming the Flash, and everything he did since he gained his abilities, would certainly count as that.