The biggest reason as to why the Crusade isn't interfering with Pandaria is most likely because of the Alliance-Horde war that will rage across the continent. They have sworn to remain neutral and given that most of the conflict that takes place across Pandaria comes to be because one of the factions. The Sha arrives mostly because of what the Horde and the Alliance brings to the otherwise relatively peaceful continent. To send a massive force to fight this would be idiotic for a faction who prides themselves in neutrality. They are also focusing on restoring the Plaguelands and while for some reason Freedom refuses to do the Risen events there's still some threats which means that they cannot send away everything they got.
As for the cities you mentioned, Hearthglen is obviously captured. Tyr's Hand was captured for the Argent Crusade but I think we lost it..? Or it was retconned and given back to the Scarlets. I'm not really sure, that city goes back and forth a thousand times over. You have to ask the staff about that one. Stratholme is also a little bit confusing because we can't do the Risen storyline. I'm not sure if it'll happen in the future or not but again, you need to ask the staff about that.
Also, if you have an Argent character you are still more than free to partake in the war across Pandaria as long as you remain neutral. You just won't have a massive army supporting you. The Argent Templars walks around Azeroth smiting evil so it should be easy to come up with a reason as to why your character joins in to fight the Sha.
As for the cities you mentioned, Hearthglen is obviously captured. Tyr's Hand was captured for the Argent Crusade but I think we lost it..? Or it was retconned and given back to the Scarlets. I'm not really sure, that city goes back and forth a thousand times over. You have to ask the staff about that one. Stratholme is also a little bit confusing because we can't do the Risen storyline. I'm not sure if it'll happen in the future or not but again, you need to ask the staff about that.
Also, if you have an Argent character you are still more than free to partake in the war across Pandaria as long as you remain neutral. You just won't have a massive army supporting you. The Argent Templars walks around Azeroth smiting evil so it should be easy to come up with a reason as to why your character joins in to fight the Sha.