Can someone become a better writer through self-practice or is feedback and critique from others necessary?

This is a really good question.

Practice is important, but if you practice the wrong thing you just get better at doing the wrong thing.

Periodic feedback helps you stay on the right track, and so does looking at other people’s work.

The best example I’ve seen came from two friends of mine who started playing tennis at the same time. One got coaching, the other just wanted to learn on his own.

They both played around the same amount, but after 6 months the friend who got coaching was way ahead. Even more interesting, after the first 6 months the “learn it myself” friend basically stopped improving entirely while the friend who got coaching continued to get better and better.

Definitely get feedback. And importantly, get it from a pro, not friends and family or randoms on the internet.