It’s obviously a combination of all three. Let’s start with the latter.
One could say my 7.0 team mate is doing all the carrying. Suppose it’s true and that he’s the only reason why we’re winning matches. Let’s say that explains the win rate.
I still have a 3.6 K/D in the Tiger II Sla over all those matches though. Clearly I’m getting plenty of kills. With a heavy, while playing it outside of its bracket. Why? Because the tank is damn good, that’s why.
Also, if you really want to know if I’m contributing to the wins or not, all you gotta do is look at the average score I’m getting with the 6.7s at 7.0. For example, my average score this month was:

This gets us to points 1 and 2. I think I’m a good player of ground, I try to improve all the time at any rate. But I would not be getting those numbers if the tanks were trash. The really good players, I’ve seen them do well in literally anything. But I’m not one of those. The Tiger II Sla, Tiger II and Jagdtiger don’t play themselves, but they aren’t duds, either.
It happens to all of us. The key point is though, anything that snipes at you, you can snipe right back. So long as you have good spatial and situational awareness you can do plenty good.
For example.
This is a Tiger II Sla nuke I got in a 7.0 - 8.0 match. In this match, I sniped a Foch’s cupola at 900m, I killed two Somuas and a Sheridan, among other things. Anyone can do the same thing with the same tank, because the tank is good, and it’s mostly good because of its gun.
Another match at 8.0:
Note that at the very beginning of the match I had two fast postwar tanks on both of my flanks. I was ready for them. Why? I saw the Frenchie in the kill feed, killing a light tank that had gone ahead of me, and I knew from experience where he would go next; and I heard the engine noise of the Bardelas on my left. I reacted accordingly and got them both, and when the Bardelas guy respawned in an AML, I got him again… and that’s before you get into the rest of the match, which I ended 5 spawn points away from a nuke.
Rule of three demands I post another 8.0 match. This is one that actually went pretty badly. Our 8.0s died right away, my first spawn ended with only three kills, we ended up losing the match. I still took an Object 906 and an M103 down to hell with me though!
Please understand that I’m not trying to sing my praises here, I’m singing the tank’s praises. I’m showing what it’s capable of. Some matches are point and click adventures. Use the Tiger II well and it’ll serve you well.
Tbh, to understand where you are now, all-time stats are less important than monthly stats. Since you’ve asked my opinion, I’ll go ahead and check, but without looking at your replays I can’t really say anything too specific.

I think you should focus on yourself first, and worry about vehicle balance later. I’m saying this in the kindest, most supportive way possible - you seem like a fairly average player, but we’ve all been there at some point. When someone on your team does very well, or someone on the red team thrashes your guys, go look at the server replay and see what they did differently. Best way to learn!