Why there is a huge difference between the new and experienced Vladimirs winrates?

Simple math. The winrate is already beneath 50% on people with a few games. Since people who are newer to Vlad don't have many games with him, their win/loss rates are skewed. This is why new champions characteristically have low win rates around launch.

For instance, I've played Vlad once since I bought him like 3 days ago. I won that game. So that means my Vlad win rate is 100%. If I play more games and win and lose more, the rate will even out.

Vlad most likely truly sits at around a 41% win rate right now, given that the players with the most games are achieving that.

I swear it's because of that new E... I can't stop tapping it out of habit...

One reason that I've seen is that if you're maining a champion, you're far more likely to play it into very unfavorable matchups.