You're attributing the difference in success here to Esperanto, but my guess is the key differentiator was actually how you went about studying the language and

You're attributing the difference in success here to Esperanto, but my guess is the key differentiator was actually how you went about studying the language and how interested and motivated you were. I took two years of Spanish in high school and gained more or less nothing from it. I decided one day as an adult I wanted to learn Spanish, and within a few months I could hold (very basic) conversations in Spanish. What did I do? Well, I probably did what you did with Esperanto. I started reading extensive passages in untranslated Spanish even when I didn't know the language, looking up any word or conjugation I couldn't remember. I more or less ignored grammar, except when I just couldn't figure out why something would be said one way instead of some other way. That quickly sent me down some interesting rabbit holes that even native speakers struggled to fully explain, but as a result I rapidly got to the point of being able to form reasonably complicated sentences. I started listening to stuff in Spanish. Any time I was about to ask someone a simple question in English, I'd ask myself, "so how would I ask this in Spanish instead?" I obsessed over pronunciation, and even though I'll never perfect it I'm much better than I ever was in high school. For what it's worth, my primary tool in all of this was just LingQ.