Basses are mostly in lower frequency unless you go high on the highest string or unless it's bass only. Even if it's bass only or high pitch, the frequency is much lower than 1khz (vocals) and a bit harder to hear out all the details that is below 750hz basically. These lower frequencies are sensed in deeper part of cochlea. Guitars, drums (except bass drums and some production puts Toms in lower frequency. Triggered Bass Drum are definitely well above 750hz though), and vocals are usually above 750hz (Some bands use 8-string guitars which is usually downtuned and uses bass string in the lowest so it may go lower). They are much easier to hear and mostly sensed closer to the entrance of cochlea.
If you listen to Jazz, you can easily hear what they are playing, but in Pop, Rock, Punk and especially in Metal, guitars sound covers up all the bass sounds. Especially in Metal, where guitar use heavy distortion and bass drums are triggered, it's very hard to hear the bass (especially when Drums are doing Blast Beats). if you compare Rock and Metal, you will easily understand that bass are way harder to hear in Metal. Take the Death Metal Band, NILE for example. Despite the bassline being the same technical line the guitarists are playing, if you are careless, you can't even hear the great techniques being played behind the guitars, fast blast beats on drums, and death vocals.
Now how about Jazz? Or any band that has bass solos? Yes of course, bass is amazing when it comes to solo. You can't really do slap bass on guitar unless you have a pencil-like finger that can go through narrow space between the strings. There are bassist who use picks and bassist who use fingers. Using pick will make the sound sharper, thus making them able to hear, but it's somewhat less impressive than guitar because for physical reasons (Bass guitar has larger gaps between strings and the strings are thicker which makes it harder for speed picking. Also, most common bass is 4 string, which limits the available notes unlike guitars which commonly has 6 strings). Finger playing unfortunately does not make sharp sound but rather rounded smooth sounds. This means harder to hear because the sound is somewhat muffled. That means even if you do an unbelievable fingerwork, the muffling will end up making it harder to hear in solos. Take Blood Red Throne in song called "Slaying the Lamb". Around latter half, there is a solo which does finger-sweeping, but you can't really hear it so much even if it's accurate and way far from sloppy (sloppy solos are harder to hear). Slap bass, in that case is the better option to make them hear out, but slap bass are much more like a percussion-ish lines and despite being extremely difficult and technical, it sounds nothing more than a simple basslines with additional percussion in the background, when it's not; as a result it sounds like a rhythmic line rather than a flashy solo that stands out.
Bass also physically "looks" like an easier version of guitar. Most basses are 4 string while guitar is 6 string. Of course bassist in Viraemia has 10-string bass, and bassist in Brain Drill owning 7-string bass, and bassist in Necrophagist having 6-string, bassist in Cannibal Corpse and Origin having 5-string. But usually it's 4. Also there are plenty of unorthodox Electric Guitar shapes like V and V2s, Random Star, Warlock, Firebird, etc. You can also make one for bass, but they don't really look so good (I find Warlock Basses cool though).
Summary
Basses are underestimated for several reasons:
1) Biomechanical Aspect - the cochlea and frequencies
2) Technical Aspect - Being compared; bass having rounder "muffled" sound as opposed to guitars having sharper "cleaner" sound. Bass also has limited note range.
3) Physical Aspect - Types of shapes available that actually looks good (or crazy). Also the numbers of strings.
Of course you know that a band without a bass sound like bogus. With bass and without bass make HUGE HUGE HUGE HUGE difference in a band. Actually, bass is more commonly used than guitar in pop and jazz. Unfortunately, many people take bass as necessary "back-ups".
If you listen to Jazz, you can easily hear what they are playing, but in Pop, Rock, Punk and especially in Metal, guitars sound covers up all the bass sounds. Especially in Metal, where guitar use heavy distortion and bass drums are triggered, it's very hard to hear the bass (especially when Drums are doing Blast Beats). if you compare Rock and Metal, you will easily understand that bass are way harder to hear in Metal. Take the Death Metal Band, NILE for example. Despite the bassline being the same technical line the guitarists are playing, if you are careless, you can't even hear the great techniques being played behind the guitars, fast blast beats on drums, and death vocals.
Now how about Jazz? Or any band that has bass solos? Yes of course, bass is amazing when it comes to solo. You can't really do slap bass on guitar unless you have a pencil-like finger that can go through narrow space between the strings. There are bassist who use picks and bassist who use fingers. Using pick will make the sound sharper, thus making them able to hear, but it's somewhat less impressive than guitar because for physical reasons (Bass guitar has larger gaps between strings and the strings are thicker which makes it harder for speed picking. Also, most common bass is 4 string, which limits the available notes unlike guitars which commonly has 6 strings). Finger playing unfortunately does not make sharp sound but rather rounded smooth sounds. This means harder to hear because the sound is somewhat muffled. That means even if you do an unbelievable fingerwork, the muffling will end up making it harder to hear in solos. Take Blood Red Throne in song called "Slaying the Lamb". Around latter half, there is a solo which does finger-sweeping, but you can't really hear it so much even if it's accurate and way far from sloppy (sloppy solos are harder to hear). Slap bass, in that case is the better option to make them hear out, but slap bass are much more like a percussion-ish lines and despite being extremely difficult and technical, it sounds nothing more than a simple basslines with additional percussion in the background, when it's not; as a result it sounds like a rhythmic line rather than a flashy solo that stands out.
Bass also physically "looks" like an easier version of guitar. Most basses are 4 string while guitar is 6 string. Of course bassist in Viraemia has 10-string bass, and bassist in Brain Drill owning 7-string bass, and bassist in Necrophagist having 6-string, bassist in Cannibal Corpse and Origin having 5-string. But usually it's 4. Also there are plenty of unorthodox Electric Guitar shapes like V and V2s, Random Star, Warlock, Firebird, etc. You can also make one for bass, but they don't really look so good (I find Warlock Basses cool though).
Summary
Basses are underestimated for several reasons:
1) Biomechanical Aspect - the cochlea and frequencies
2) Technical Aspect - Being compared; bass having rounder "muffled" sound as opposed to guitars having sharper "cleaner" sound. Bass also has limited note range.
3) Physical Aspect - Types of shapes available that actually looks good (or crazy). Also the numbers of strings.
Of course you know that a band without a bass sound like bogus. With bass and without bass make HUGE HUGE HUGE HUGE difference in a band. Actually, bass is more commonly used than guitar in pop and jazz. Unfortunately, many people take bass as necessary "back-ups".
