I think this deserves an anecdote. The greatest classical bassist I've ever met is the woman who plays bass in my fathers bluegrass band. But she wasn't always a particularly great bluegrass bassist.
She came into the band via her husband who's a noted (Well at least in the local scene) bluegrass mandolin player, when they met and fell in love she had never even heard bluegrass before (Despite being a Kentucky gal) , and although she apparently enjoyed watching the musicianship of her husband was not initially particularly enthused by the bass generally typical to the style (often simply a i-iv-i-iv kind of thing).
Now, this woman is an astonishing classical bassist, for many years the lead soloist bassist in the state orchestra here, this woman reads flawlessly, had a masters degree in music (but for some reason had never done any significant jazz improvisation, I guess the music degrees where done differently back then). Watching her play was mesmerising. Let me be clear, she was exactly the sort of musician you refer to here.
But when asked to join her husbands bluegrass band on bass was absolutely terrible at it, despite it being an incredibly simple genre to play, for a bassist. Myself, 10yo (this was 30 years ago!) son of banjo player, hater of anything not heavy metal(dont worry, the last 30 years have seen my tastes evolve a little lol), had a significantly better feel because at least I had grown up in the groove of the thing. She really struggled with it. Not because she couldn't memorise the songs, her brain was built for THAT task, nor because she'd get the notes wrong, but because she hadn't learn the groove of the thing yet. She didn't know yet how to relax and stop viewing musical as a giant mathematical galaxy-brain fractal, and just let the fingers do the talking.
In other words, she had a lot to learn.
Now, the epilogue to the analogy is 30 years later, still bassist of that band, she's the best bluegrass bassist I've ever seen. And still goddamn ascended master at the classical stuff . Probably can't jazz improvise worth squat, but I doubt she's attempted it in the last 30 years either.
My point is, an expertise in technical skills, and masterful sight reading isn't anything approaching the end of a musicians journey, its barely even the start. It might even take a genre as famously unrefined and simplistic as bluegrass to stump a master sight reader, because thats country where most of its legends barely had the education to write their own name, let alone a band score.
You'll never reach "the end" of music. Theres always new things to learn.