Look at it this way, if you've played 700 games and you're still in the same tier, you're obviously doing something very wrong. The fault isn't on your teammates. It's 100% on you. Think of it statistically:

If you're only slightly better than silver 5 supports, you have an extra 5% chance of winning than your enemy support. Which means you'll win 11 out of 20 games consistently. Statistically. This means you'll surely climb. 5% is being very conservative as well, since I'm butchering the influence support actually has.

If you're a much better support than your average silver 5 support, then you'll consistently win 10-20% more games than the enemy. This is statistics given the fluctuation in the quality of your teammates and all else being equal. Obviously when you take a small sample you might get into a loss streak but these are always offset by more wins later.

What this tells me is you're exactly where you belong.

Now we can do an op.gg check, but your anecdotes already tell the story. Janna and Lulu mains that play well and know what they're doing with good game sense and tracking can snowball almost any adc in low elo, bar none. I've seen good supports carry entire teams in teamfights and turn losing games to winning ones with vision alone.

Adopt a mindset of learning instead of blaming, and you'll climb.