So do you have to win at least 50% to even rank at all? I can't seem to squeeze out level 1. I win about 33% of my games.
Depends on whom you play. If you mostly play opponents of your level, and win 50% of you games, your mean skill will stay the same, but your variance should decrease, so you gain levels.
Your
graph looks like you lost 10 levels due to increasing variance in half a year of not playing, but afterwards your mean level increased and variance decreased, so probably, when you continue playing you will get positive at some time.
Edit: In a quick look it seems to me that you buy too many terminal actions. So if you priorize Silver a bit higher, you would probably win more games. If you look at your games (see link above for old games) how often you draw at least 2 actions, but can only play one, and imagine every time that happens one of them would be a Silver, your hand looks a lot better...
Edit2: Actions are fun, but having two of them in hand an one can only play one of them is not.