The online Music Theory class that I’ve been taking has placed a lot of emphasis on reading and comprehending sheet music. I’ve learned a lot as a result, but I’ve also realized that in today’s world, with audio recordings so readily available, a more practical understanding of music theory is less about reading and writing music and more about developing a vocabulary so that you can apply meaning and understanding to the sounds you are hearing.
Being fluent in sheet music can be helpful, for example, in a situation when you need to immediately start playing a piece without having first acclimated yourself to it or knowing how it sounds. But with sound recordings to supplement the written score, there is a less of a need to convey all the complexities of the music in the written form when a lot of it can be explained intuitively upon hearing the piece.
Tommaso Zillio of the site musictheoryforguitar.com has this to say on a similar topic:
Learning music theory and training your ear go hand in hand. Trying to do only one is like trying to ride a bicycle without one wheel: useless, overly difficult, and a guarantee that you will hurt yourself. In fact I do take the radical position that ear training and music theory are in fact the same thing.
If you think about it, all music theory concepts can be explained as "If you do X, that's how it sounds,” "if you play a cadence, it sounds this way," "if you play the notes of the chord while improvising it sounds this way," etc. As you can see though, if you don't know what "this way" is for every single concept you learn, then you are not really learning much!
This is why there are a lot of people who say that music theory is useless: they didn't connect the formal aspects of music theory with the actual reality of music. After all, a map of your city is useful only if you know the relationship between the funny lines on the paper and the actual streets. Luckily, there is a very simple solution for that: every time you learn something new in theory, PLAY it. Make sure you have at least 3-4 examples for each concept you learn (you can compose them yourself in case).