Aside from Knicks who uses Superman as much as he uses Darkseid, nobody uses Darkseid exclusively, not even as a secondary character. The game was released half a year ago. If Darkseid had been top 10 in any previous version of the game, a high level player would have certainly learned and placed with the character, but no one did. The reason is simple. There have always been superior options. If I want extremely good zoning against melee characters, I can learn Deadshot or Captain Cold as some high level players have done. If I want offensive tools that offer high reward and low risk, I can learn Black Canary, Catwoman, or Flash as some high level players have done. Darkseid neither exceeds in nor offers any innovative gameplay in any specific match ups. I doubt the next patch will change my perspective, but he is merely a high reward and high risk character who has good zoning but no footsies presence whatsoever. Believing that he is a mid tier character is counter-intuitive if you base your opinion on special moves and damage output, yet the evidence clearly points in a different direction. No high level player uses him. No high level player places well with him.
As far as history is concerned, the community remembers when you are wrong but forgets when you are right. When I was preaching how broken Smoke was in Mortal Kombat 9 or Martian Manhunter in Injustice 1, nobody cared, yet everyone seems to recall the inaccurate predictions about Zod and Tremor to this day.