Yeah, playing outside of your comfort zone is the ONLY way to improve.
Nothing ventured - nothing gained, huh?
.
At least 50% of all the new songs I write contain a new chord or a new technique for me. . . . or something I can't do so good . . .
I am unable to adequately play about 65% of my last 10 songs.
. . . yet . . .
Many of my songs take me 3 - 12 months of practice before I'm willing to play them in public.
Still, I gain a new 'public-song' every 2 - 3 weeks.
And most of these songs have something in them which I couldn't play a year ago . . .
Originals or covers - same thing.
Find music that you can't play, and try to play it anyway.
It all mostly comes from determination, a willingness to work, practice, and, maybe, a little bit of natural ability. You CAN improve what you are able to play. No matter WHO you are . . .
You may or may not approve of your attempts . . .
. . . BUT . . .
Play outside of your comfort zone, and you WILL get noticably better.
It all comes down to WHAT you practice, huh?