RE: Is a prime lens a prime choice?

Stop.

If something needs to be "improved", more equipment won't help. Not a bit. Paraphrasing line from a popular photography site, "more/better equiment does not necessarily correlate positively to better shots. It does, however, make taking great shots easier."

You take the shots, nothing else.

Back it way out, to fundamentails of composition, mechanics of cameras, etc. then start taking steps forward, assuming you'd like to actually "improve" the shots.

I personally found a combination of self-study, classes, and trial-and-error the best way to up my game. The latter being by-far the least-efficient way to do so.

I'm not Ansel Adams, nor do I sell my work for a living, nor did I ever seriously shoot film. But I've sold a few items, past several years, and was fortunate enough early-on (c. 2006) to not buy too much equipment before discovering I didn't know what the hell I was doing. I'd moved from "snapshot and pos" to "DSLR" that year.

Amusingly enough, eight years later (2014), I migrated to a Fujifilm X100T: truly a shooter's camera, with echoes of Leica's rangefinders in the build quality, look and functionality. Leave it to the Japanese to once again beat the Germans at their own game, at 1/5 the price and at least the same quality.

Point being, that X100T compels me to focus (bad pun) on ISO, shutter speed, exposure, and aperture. I cannot easily duck any of them, the closest it comes to "Auto" mode is "Program" which adjusts aperture and shutter speed. The rest is always up to the photographer.

Amazing what one can learn with stellar, and subtle, equipment that forces thoughtful composition. Food for thought.