I dont know about that. 'Iconic' means that even without watching the material, you know who the character is. Without ever having seen a cartoon with him in it or having played Kingdom Hearts, you know who Mickey Mouse is. He's iconic. Same with Batman, Superman, and Spider-man. Hell, they're so iconic that people are practically born with the innate knowledge of those characters' backstories; that's iconic.
Steve though? Nobody who's never played the game knows who Steve is. They can recognize and name Creeper, partly because even if they had to guess, they'd call it some kind of 'Creeper', but Steve? They just assume its the generic player character. I, for one, had no idea there was even a named character. I thought it was just a blank avatar.
Not to mention that I think its a little too early to call a game that came out less than 10 years ago 'iconic'. If Minecraft is still relevant and highly recognizable 10 years from now, then we can call it Iconic. Its a bit too early right now; I would just say that its popular. And even then, it's popular only with a given age group.
Just to put it in example, Minecraft is primarily played by people 21 and younger (the percentage of those who play reduce pretty heavily after 30; down to single digit percentages according to a survey done by Microsoft in 2015) whereas people of all ages and ethnic groups recognize Mickey Mouse, Batman, Superman, and Spider-man. I'm not even including the other Marvel heroes, because until the MCU, even Ironman wasn't too well known (heck, the company was about to go bankrupt in the 90's and the only reason they survived was because they sold movie licencing rights to both Sony and Fox for their characters).
Those are iconic characters; characters who people can recognize and identify just on sight decades after their initial introduction. I'm not knocking on Minecraft, but Steve is no way near what one could consider 'iconic' yet; he's just from a popular series right now.