I made the most progress in my musicianship by learning about other instruments, and by learning to play a bunch of them.
In addition to being able to play bass guitar I can also play Double Bass, Cello, Violin, Drums, Piano, Saxophone, Flute, Trumpet, Trombone and Guitar.
I have gigged and recorded on most of them. By learning other instruments, my awareness of their functions in ensembles, pitch and dynamic range enables me to orchestrate and arrange parts appropriate for a given instrumentation. Multi-instrumentation allows me to be able to communicate to other instrumentalist far more effectively, such as those instrumentalist playing transposing instruments.
All the knowledge I've acquired informs my bass playing to, for example my knowledge of harmonics does not come from listening to bass players, the harmonic note options of a given fundamental come from playing brass instruments particularly trumpet, the execution of false harmonics come from guitar.
The reharmonization knowledge I've gained comes from playing piano.
Overall I recommend learning other instrument to understand music from a more informed perspective.
It helps transcription also, I can check it a lot easier, I have transcribed many horn solos and then learnt to play them on bass.
Of course I learnt to sight read, jazz theory and different styles of music too. None of it happened overnight it's been a 20+ year journey of learning.
Even with all those instruments that I could play, I still find bass to be the one I feel most at home with and I like that because it is such a new instrument it feels as though there is many innovations yet to happen, in my opinion at just under 70 years of existence it is still in the infancy of it's development.