There is without a doubt that Mirage is a weaker Champion than A lot of them, He holds no real benefit to the team and is very much a solo character. Yes, the buff to his revive and respawn is good but its still doesnt make him anywhere close to other characters like Wraith, Bloodhound, Lifeline or Gibby.
Mirage is just a gimmick character. its easy to tell which one is real or not. Im a Diamond 3 player slowly climbing and I am yet to see another mirage.
For example, when he is reviving someone, he goes invisible, but what does it matter when everyone that is close can hear you reviving them. Lifeline has a shield and auto res. Making her infinitely better than mirage already.
His Ultimate is pretty predictable too, the blue glowing lights are annoying and people can follow them.