A well-designed matchmaking system should leave you with a 50% winrate. That's how Elo and Elo-like ranking systems are designed to work.

If your Elo is climbing over time, that's (probably) good progression. If your Elo stays stagnant with a 50% winrate, that's you not getting good. With the caveat that how "good" a particular Elo is can change over time, since the starting Elo is by definition the average. If existing players are learning to be better, or worse players are quitting the game, or better new players are joining, remaining at the same Elo might mean you're actually improving; you're just improving at the same rate as the average player. And conversely if more casuals join or hardcore players quit, the average should go down.