WARNING: The following contains spoilers for current seasons of The Flash and DC's Legends of Tomorrow.
The Arrowverse has a lot of characters in its large roster, but they manage to handle them all fairly well. Everyone has their moments where they stumble, such as Arrow's Laurel Lance for...okay, most of the time she was on that show. But all in all, the cast and writers know what they're doing and make sure to do justice with these decades old characters. (Or, at the very least, find something new and inventive to be done with them.) However, one such character who stumbles, and quite often, is The Flash's Wally West.
Introduced in the middle of Season 2, Wally was the secret son of Joe West and his then-wife Francine brought into the fold of the West family. Despite initial misgivings between him, Joe and his sister Iris, he almost instantly became a true member of the West inner circle. When the reveal of Wally was first announced, many fans went wild over the possibilities of him on the show, since this came just a few years after the New 52 had revealed the new DC Comics version of Wally was also black.
Unfortunately, Wally soon found himself in the role Iris held for most of Season 1: Forever drawn into the crazy loop that is Central City's metahuman problem, though not enough to really be a part of Team Flash, even though he really should be. If you go back and watch Season 2, it's actually kind of astounding of how often Wally straddles the line between being part of Team Flash but also not, even while he's dating the daughter of a guy from another universe and has a speedster threaten to kill him. For the first third of Season 3, that status continued, even though he'd gotten speed powers of his own thanks to Barry's Flashpoint meddling.
Keiynan Lonsdale plays him real well, but Wally is just saddled with being unfairly regarded by the show as a second stringer at best, and has been knocked down another peg this year thanks to the recent arrival of the Elongated Man.
Even when Barry was stuck in Speed Force jail and Wally took over as top speedster at the start of Season 4, the situation barely lasted long enough for it to feel like a real change before Barry returned to don the red and yellow again. The bottom line is, you could cut Wally out of the series entirely and, sadly, not a lot would really change. In battles, he's always conveniently knocked out or conveniently beat down so he's out of commission. As a result, when Wally decides to leave the show for a few episodes in the first half of Season 4, his departure is nowhere nearly as interesting or earned as the writers seem to believe.. Then, when he does come back, he's immediately sidelined in both the Crisis crossover and the previous week's episode.