junkrat → no skills, low mobility

let me tell you about concussion mines and a two little things called surface deflection and gravity.
sure everyone can stand behind a wall and spam bombs but it takes less skill to play as soldier, ana, D.va, Mecree, reaper, tracer, etc, because they don't have to deal with travel time nearly as much as junkrat does, even pharah takes arguably less skill to play even though she has more travel time on her main fire than any of the heros I just mentioned.

Good junkrat players have to think about how high to aim for maximum hight and length as well as taking into account that the bomb can deflect off of three objects before it blows up.
and then there is the lovely little mine he has, a sweet tool to send you or the enemy flying.
with it you can outflank enemies, get out of tight spots and even get right up in range to hit those flying pharas.

compared to other heros playing junkrat is like solving a math equation everytime you shoot.
or you can be a noob junkrat and just fire bombs over cover and cross your fingers they hit something.

Yeah, Junkrat has an incredibly difficult time taking down a Pharah. That's what hitscan heroes are for. The only thing Pharah really has on him is mobility and range. However, her mobility makes her an easier target for hitscan heroes, while Junkrat can attack while behind cover.

It's basically Soldier vs Demoman.