There's a few problems with your tier list.

Problem 1: You don't specify which game mode. You say "individual performance" but honestly if this is a Solo Queue tier, it's far off. If this is a premade tier, it is again, very far off. Different tiers of difficulty would also have different tier lists, as some classes are super good at stomping nubs while others are more effective against organized teams.

Problem 2: You offer little explanation for your choices, which makes it unclear why you believe them to be strong. By looking at your list, I'd say you chose the classes to be "S" tier just because of their CC and ability to shut down other classes. Also saying "counters" doesn't really apply for some of your tiers, especially DRK. It's not that DRK doesn't have counters, it's just that the class lacks in both damage and utility.

Problem 3: Another way it seems that you're measuring this is by a classes potential, not so much their effectiveness. For example: In a perfect condition, sleep is probably the most powerful spell in PVP. This is why I'm assuming you placed WHM/BLM in S-tier. Realistically, sleeps will be purified (or broken, if we are speaking Solo Queue), so their effectiveness is reduced, especially on WHM where every GCD counts during heavy burst.

Problem 4: MCH is easily the most broken class in the game right now for PVP, and you have it at...Tier B? It shows inexperience on your part. I'd say instead of making a tier list, a discussion should be had around making said tier list.