Although I'd be an idiot not to agree with the basic fundamentals of this "oft-used" phrase, it's also a lot of crap.
Yes, dynamics, volume (to a degree), and transient attack are in the hands (which is why I don't use a compressor). Also, based on the position of the plucking fingers (closer to the neck or closer to the bridge) the tonal character of the fretted notes can be significantly changed.
However, my "hands" will not dial in differing degrees of overdrive if I want. My "hands" will not give me a "chorus" effect when needed. My "hands" will not give me a bass boost, or midrange scoop, or bright attack, or tube break-up like my Genz-Benz heads do with the mere push of a footswitch. My Peavey 115 BVX-BW sounded very different from my current Genz Benz Neox 212t. The Peavey had excellent low end Whoompff, but my GB sits in the mix much better than the Peavey ever did. I'm really not sure how I would emulate that difference with only my "hands".
The electric bass guitar is only the first point in the tonal signal chain. The electric bass instrument is half the signal chain, the other half is your amplifier. After the signal leaves your bass via the instrument cable there are a whole lot of other useful and unique ways to vary the tone. You may not use them, but many bass players do.
Instrument
- "hands" (how you cause the string to vibrate)
- vibrating string
- pickup
- blend control
- active preamp
- active / passive tone controls
- master volume
Amplifier Rig
- bass preamplifier
- tone controls
- effects
- power amplifier
- speaker cabinet/s
The above doesn't even get into the subtle ways in which preamp gain and output interact with the power amplifier and the master volume. Nor have I gone into "10's vs 12's vs 15's" discussions. Just trying to keep it as simple as possible.
My preference is to take my GBE750 or ShuttleMAX 6.0 post pre DI out to the board and to give my rig only enough volume so that me and the drummer can hear. The soundman can do what he wants after that. In my experience, it's usually the guitar amps that are too loud.
Last year around this time my band played in a large concert hall with a very big professional PA system.
I was presented with a DI and a Fender Rumble 100 for monitoring. As the band did the soundcheck and they dialed up the monitors and subs I heard the usual rock concert characteristic bass tone. Overly-loud, indistinct, rumbling, boomy, can't-make-out-the-pitch-if-you-tried, billowing bass. The little Fender combo wasn't able to keep up with that. Thankfully the monitor mixer was a very nice young lady who (when I asked nicely) turned up the sidefill on my side with a little "more-me" and I was at least able to hear myself despite the poor tone for FOH. Sorry for the long rant.