If they were to take a break from speedsters as the 'big bad' what other villains could they use? I haven't read the comics so I'm only aware of the main ones like the reverse flash and mirror master.
I feel like @gorogues would be able to provide better insight here, but off the top of my head?
They could’ve made better use of Grodd, a very important Flash villain, and made him the ‘big bad’ of a season instead of a mid-season villain. Gorilla City (aka, the gorillas attacking?) could have been something they led up to for a season finale, and had the Rogues help fight the Gorillas with Team Flash, sort of like what happens in the New52.
(Personally, I also think the military and Eiling makes for an interesting villain but maybe not a seasonal Big Bad, and shows have to be careful about just how thick they lay on the anti-war anti-military message).
They could’ve done a lot more with Dr. Alchemy than they did. I know a lot of fans of Alchemy have been disappointed that he was just a pawn for Savitar. Alchemy = squandered potential.
They could do more (like a lot more) with the Rogues. It’s tough in the sense that the Rogues are often just hoping to steal stuff and don’t have any truly evil designs, but there have been internal conflicts within the Rogues and big blow-outs, not to mention that they can be pretty menacing when they’re altogether. Teaming them up with the Reverse Flash is an interesting route (or with Inertia, but uh, I’d rather not see Bart die, like what happens in the comics).
So… I’m sure there’s more. But there’s those already, off the top of my head. Speedsters are a huge part of the Flash and tend to be some of the Flash’s greatest enemies, but aside from Reverse Flash, most of them aren’t super specific to Barry’s own arcs.