"I have been learning Spanish for over three years now ... However, I really struggle with understanding spoken Spanish." In this person's case, it could be that they've spent three years on duolingo instead of practicing listening to native Spanish speakers. I've been learning my target language for two years and have no difficulty understanding it when spoken. Over that time I have listened to hundreds of hours of…
It doesn't matter their method of study, the question is legit nonetheless. Spoken language is harder to learn.
I think you'd probably learn more from the spoken language. Spoken language is higher bandwidth. Tone of voice, melody and rhythm can convey a lot of extra information with the same words. Plus if you're getting the spoken language in real life or from video, there's probably a bunch of extra context that makes it easier to understand. Even better, if you're talking to someone willing to help you learn, they will simplify their speech and start using gestures to help you understand.
I can accept that, as in the article, for someone who's spent all their time on written language spoken language will seem harder. I've split my time equally between the two and neither seems "harder" than the other. For what it's worth, my target language also uses the latin alphabet.