Brian Wilson's an interesting case. As most know, he was almost completely deaf in one ear, and yet is widely regarded as one of the best mix engineers of all time. When most contemporary bedroom mixers are directing their efforts at getting stereo width, you've got to wonder how the heck he pulled it off.
Like many of the legendary mixers, he started out in a mono world. The Beach Boys saw their first commercial success in 1962, a time when 99% of record purchases were mono, when very few consumers owned stereo gear, and most music was listened to on AM radio. Even into the mid-70's, it was common practice to do the mono mix first,
then a stereo version.
Consequently, all mix engineers of the era were more adept at mono mixes than stereo. Unfortunately, it almost became a lost art starting in the 80's. But it was eventually rediscovered. People realized that if you got a good mono mix first, turning that into a good stereo mix was easy. Today, it's once again common practice to mix in mono first and
then stereo-ize it.
One way that's done is to use a mono speaker. You (Jesse) don't have to, as you're hearing essentially mono all the time. You have the potential to be a very good mono mixer! So don't worry about it - make the best mono mix you can and then solicit the aid of another set of ears to tweak the stereo version.
No, I'm not suggesting you need someone else to do the stereo mix for you, only to provide feedback and suggestions. You can visually apply stereo effects yourself because
a good stereo mix also sounds good in mono. IOW,
you'll know if you're screwing up the balance.
On a related tangent, all of us are gradually losing hearing acuity. As we age, the tiny hair cells in our cochlea are dying, reducing our ears' ability to respond to high frequencies. To make matters worse, both ears don't age exactly the same, so our frequency sensitivity becomes asymmetrical. Statistics show that audio engineers lose their hearing faster than the general population, so we have to adapt.
Fortunately, the digital age has provided us with visual aids. They should not be dismissed as cheats! When I hear guys mindlessly repeating that tired "trust your ears" mantra, it's like listening to somebody insist that global warming is a liberal conspiracy. I don't care how good your hearing is, you
cannot trust your ears (or, more accurately, your brain). Everyone should learn how to use visual aids properly, not as the sole source of information but to augment our unreliable ears.