This is based on personal experience and preference. When it comes to learning, the disadvantage of using a non-prefered language as a basis is unimaginable for anyone who hasn't done so before. It can easily lead to a resentment towards certain topics since massive amounts of time would have been wasted by it.
As an example, when I moved back to Germany, my level of German understanding was almost nonexistent. I could at most formulate the bare minimum of sentences such as "My name is ...." and "I am ... years old." Due to the requirements of German schools, I had to learn an additional foreign language which ended up being French.
It's somewhat hard to express the full magnitude of how difficult that can be.
Imagine needing to learn new vocabulary, using words that you don't recognize. Basically always needing to do double translations (which are obviously quite inaccurate). Now add on the stupidity of genderized words and you'll be in for a world of pain. The German language uses 3 gender pronouns for words; masculine, feminine, and neutral (each word is assigned one of the genders). French uses 2, masculine and feminine. Of course the genders for both languages are seemingly random and they don't align.
It really makes you appreciate the simplicity of the English language.
My level of German understanding was so low at the time, I only realized near the end of the school year that we actually had a booklet with french grammar rules that we had apparently been learning from.
Looking back, I'm surprised that I never failed a single class due to the sheer absurdity of the situation.
[There was definitely a point in time where I straight up detested French and everything that had anything to do with it. Had I learned French using English without the added stress of German, I would've almost certainly liked the language. This is of course just one example of many.]