I thought that David Harewood was only going to be recurring next season. In which case, J'Onn won't always be available--plus he costs a lot to realize on screen in his Martian form. They should have enough super-heroes and costumed crimefighters on their roster that they can mix it up. Just as we see in the comics, where different teams of heroes will go out on a mission (for the Justice League or whatever). And there should be other heroes in National City that Alex can bring in--with so many aliens around.
I just wish, instead of the DEO, it had been the Cadmus Project from the start. And the Project were good guys, not bad guys. Then they could have Guardian and the Newsboy Legion--and maybe Superboy--plus Dubbliex and other DNAliens. Really, the more Kirby the better.