You sound like someone who plays sub 1000.

If Pharah moves, you move. You're allowed to move. If Pharab isn't in the sky then that makes her much more volunerable. If she's on the ground near your team and you're not then you're in the wrong spot and need to move.

If you're team isn't supporting you during this then the chances of a lost round is greatly increased. This goes for pretty much every role, though.

If you're a thorn in her side then she can ignore you and pound your team which means that she's easy pickings for you. If she's focusing on you then she's leaving the rest of your team alone and it's now a duel. The better duelist with better support wins.

And the biggest WTF is here.

Now that becomes your only job. Other counters, like Reaper, don't have to constantly focus one hero. He only has to hunt Winston when he dives the healers. Genji can hunt healers, but he can also do all kinds of other shit.

After you kill Pharah you're allowed to shoot at other enemies. Soldier is a solid pick versus most others. You're acting like after Soldier kills a Pharah he sits around doing nothing. Soldier is an asset to almost every group. He has solid close to mid range damage and off heals.

But let's say that the match is a Soldier vs Pharah duel the whole time. That will keep her busy and keep her off of the rest of your team. It's a solid solution to the problem where in between the duels he's still an effective memeber of pretty much any team.

Using Soldier to counter Pharah does not hinder your team. What point do you think that you're making here?

Countering is what the game is based around. Several Heroes need counter picks to keep them from being too much of a headache. Genji, Widow, Tracer, Doomfist, etc. Leave them uncountered and they can wreck you, especially when pocketed. That idea isn't unique to Pharah.