If in 6 months you learn 6 small pieces that is a pretty good learning rate to start off with, one a month. Of course you want to be able to increase the rate at which you learn and constantly challenge yourself with new experiences (this can be hard to do yourself unless you are nautrally musical). You should try to play your violin music on your piano, that would boost your learning curve imo without much effort.
Learn something from Bach and Czerny. Since you are on Bartok try his famous 6 Roumanian Folk Dances, learn the melodic lines and play them with the correct articulation. The 2nd one easily could be learnt entirely. Bartok's Train Journey is good to initially develop ostianato. Try Kabalevsky's Clowns.
If you plateau in your musical development you have to question what the heck are you doing wrong. Sure we can get uninspired to learn that is a natural lazy human response (and physics, a body that is at rest wants to stay at rest

), but we must always realise we are always improving and getting better, if not then you need a teacher to prove this point to you and make you study music in an effective way. Your personal excitement in the investigation of sound with your instrument should be the inertia that makes you move on in your music not get bored with your musical production.
Try not to compare yourself with anyone when it comes to music. This sets you up for depression or a false sense of superiority. Of all my students that I teach and teachers I associate with, some very very good pianists, none of them study as much as me, or know as much music. Does that make me feel confident and happy and good about myself? Hardly. I know there are other people who know a great deal more than me! And I know there are people who might not know as much as me, but have specialist knowledge in areas I haven't even touched! But all this doesn't matter. The world is pretty big for all of us, no one will overshadow your musical career, it is not like a monopoly of only 4 master pianists conquering the world. The music world is much more diverse and SHARING.