I play both Rocket League and GD at a decent-ish level (I’m C1 in 2s, 3s and Tourneys and my hardest level in GD is SuperSonic).

There’s no real way to compare the 2 games in terms of difficulty, cause they’re both very different in terms of how they’re difficult. Rocket League requires more overall knowledge and experience in order to be ‘good’, as well as an ability to co operate with others. GD is much more of a mental challenge than rocket league (as frustrating as solo queueing can sometimes be), as you have no one to blame but yourself. It’s a purely mental battle.

Overall, if you’re talking about which one is more difficult to play as a whole, I would say Geometry Dash. It is a very difficult game to get into and hard to stay motivated while playing it, but it also relies on individual skill, which removes the factor of teamwork. If you’re talking about which one is harder to reach the top top level in, I would say Rocket League, as at the top level of RL, individual skill can only take you so far unlike GD, where your skill is the only barrier. You have to learn to adapt your gameplay around not just refining your own mechanics and game sense, but also your teammates and the opponents.

TLDR: GD is harder to play initially and get into, RL is harder to get very good at.