Am I the issue or does matchmaking just really not like me?

Just as the title says, I just don't understand why I can't rank up. I've clawed my way from Bronze 5 to Plat 5 over the last 10 seasons, but I just cannot seem to get past this rank. The last 3 seasons I've been stuck between Plat 4-5. I hit 4, then go back down to Gold 1, repeat. Over and over. I feel like I'm getting horrible tanks, but I've gotta wonder... am I the issue? It's been 3 seasons, surely matchmaking doesn't hate me that much, right? And if I am the issue, what is my issue? What could I improve in order to climb higher?

For more context, I typically play Kiri/Mercy in competitive. I can play pretty much any support, bar Zen for some reason. I only pick and stay on Mercy when I recognize there are good dmg boost targets and my DPS are doing well. I swap to counter if needed, and don't like playing just those 2 tbh, so I sometimes just play who I feel like unless we're doing very poorly. I just can't carry when my tank is 0-11 and opposing is 30-0. It's frustrating, I want to climb but I feel so stuck because I'm solo queue.

Here are a few replay codes, please give me feedback on how to improve. I'd like to hit Diamond, I don't want to be some GM level player. I just really, genuinely love this game and want to be better at it. My username is Kizusuita.

Brig/Moira/LW (Win): DBFCSA

Mercy/Moira/Brig (Win): KBQEAZ

Kiri/Moira (Draw): 3HEWCP

Mercy/Kiri (Loss): KWWG0E

Mercy/Kiri/Ana (Loss): Q393CD