When I was in my early teens I did both English with a cipher and Americanized Norwegian with a cipher, then I moved on to making an actual conlang that was shitty, then an actual conlang that was a little less shitty, then an actual conlang that was decent, then an actual conlang that was good-ish, and I've been slowly refining that one for many years now.

There isn't anything inherently wrong with making a relex (i.e. the writer's first language but with a cipher or word replacement), but there is a time and a place for it. Some people don't care about linguistics and they shouldn't force themselves to care, because it's going to show.