Anecdotally
Many years ago I watched an excellent documentary about violinists in which Itzhak Perlman likened the violinist's bow to an "artist's paintbrush", describing how each requires "a lifetime to master". Likewise, I have personal second hand anecdotes from Pinchas Zukerman saying things like the symphonic orchestra is the greatest of all instruments, and that when someone asks you what you play, you should respond that you "play the bow".
From my 24 years of viola playing, I can substantiate these two metaphorical idioms about the bow with my own vicissitudes of the bow kind.
Violas
But first let's discuss the more significant differences between violins and violas. Violins are almost ridiculously small. Every time I pick one up and play it, it feels as if I'm holding a toy. But thus compared to the viola this toy holds two very important advantages:
Being smaller means that I can practically dominate the entire fingerboard from 1st position, or if necessary shift up into 13th position without any care or effort.
The smaller size means that the response time (the time between initiating bow movement and the instrument achieving steady-state resonance), at least for a well-made violin, is vanishingly small. A skilled player can move from ethereal to furious to euphoric to bucolic instantaneously and all in the same phrase, even.
Going back to the viola, you realize how comparatively unwieldy is its size and acoustical-mechanic hysteresis. Both imply a small, but appreciable effort for each action or style change. Playing a note on the viola requires you to make micro adjustments in the left hand finger position, angle, and pressure to be followed by the highest care in placing the bow relative to the string, adjusting the hair angle, finding the correct contact point along the string relative to the bridge and along the bow relative to the center of mass, and then calculating the perfect shape of bow attack and drawing the bow fluidly across the string using the correct bow speed and arm weight. This is all in addition to the interrelated two dozen posture and form techniques that must be mastered before any serious study of the instrument is begun.
Even the strings on a viola being longer means that micro adjustments to left hand position for intonation are larger, slower, and more difficult, and the strings being more widely spaced makes each string crossing that much more treacherous. Every instrument has a joke about how it's not played in tune. The viola variation of this idea seems to be something like "always being tuned, but never being played in tune". Only a violist is really going to understand what this means as it grossly controverts the multitude of diligence in simultaneous skill required to produce any note at all on top of what you would already baseline expect for a violin.
Good players and instruments will naturally have easier times overcoming and mitigating these challenges. For example, the most expensive viola I have ever tried (German, 1880s': $163k) had by far the shortest response time I've ever experienced.
It's the Bow that Chooses the Instrument
Now that we've gotten the violists' apologetica out of the way, let's talk about bows.
One more anecdote: The late and beloved Peter Prier, proprietor of one of the first, if not the first, violin making school in the Western Hemisphere, described the relationship between the instrument and the bow as a "marriage". For many years, my only instrument was a student viola my parents got me in high school and it was a chore to play on. About its only quality of redemption was that it looked well enough. I was finally able to afford a real instrument only a year ago. Buying a bowed instrument is a two part process, not only because bow making is its own trade, but also because a caring and attentive musician must seek a proper mate for their instrument. I was able to find a matching bow in about 2 months. The experience was like the finding of a wand a nascent wizards as he embarks on a lifetime of devotion to the craft must have had. It was not the most expensive bow I tried, but in ways that still mystify and enchant me, upon picking it up, it seemed to feel light and warm in my hand, the sun shone a little brighter and the birds outside sang a little sweeter and the colors of the world were a little deeper and no sight or object went untinctured from an ubiquitous, subtle beauty. It drew out of my viola clarity and focus while enhancing the instrument's intrinsic warmth and brilliance. When I stopped, my face was hot, my muse quickened, and I knew I had found The One. Going back to my student bow was like trying to bow with a hack saw. Analogously, I tried the same two bows on my old instrument with almost no perceptible difference.
From Good to Great
This analogy of instruments and bows leads to my next point, which is that the difference between a good student and a great master is both big and small, or rather, that the making of great music is all done in the minutiae: small quantifiable differences in wood quality and craftsmanship, kinesthetic control, aural feedback, and sense. One may measure these differences with crude tools and conclude with the expected small discrepancies, but that is because the profound differences are much smaller still. A great master has control over the tonal center down to the last overtone beat fraction, vibrato to like the 19th term in Fourier decomposition, and most of all, the bow inflection down to the last neuron in her hand.
There is a temptation, especially in orchestral string sections to over-prize these minutiae from the unified symphonic narrative and copiously or fastidiously annotate the written music, like a lawyer unseemily burdening banalities with confounding boilerplate. Any musician can tell you that excessive annotation encumbering the page, even if it does not obscure the notes themselves, will distract enough to make the copy seem unbearably unreadable. Similarly, a preoccupation with bowings is frustrating when it means the whole section has to rebow parts of the music right up until the dress rehearsal. There really is no perfect bowing, and a corollary of this is that a good musician can make almost any bowing work. I have seen some really funky bowings in my time, but none of them compare to the distraction of rebowing a part mid-rehearsal or of the value of the lost rehearsal time. It is true that minutiae are what matter, but once you cross the threshold of ephemera, your part annotations are going necessarily change every time you play the music and you music will be be that much less intelligible. Because making music is also wonderfully spontaneous and an intimate, transcendental collaboration of sound among peers, most of which is better left as a subtext.
The Real Heifetz
This is what I really wanted to talk about before getting distracted with my own anecdotes and contexts. I have once heard that playing "faster and cleaner than Heifetz" has been achieved in one historical or famous circumstance or other. It is true that Heifetz developed a style that allowed him to play famously fast, but if speed is what you desire, you might be better off with Hahn or if you want cleanliness, try Perlman (Note: Hahn and Perlman in their own ways are both magnificent masters of the violin). I've always thought the notion bizarre because these are not the greatest virtues of a Heifetz recording. They may be part of the necessity, but the sufficiency of the art is largely accomplished by, again, the minutiae. One does not simply agitate the bow as rapidly as possible across the strings. Rather the delectable joy of Heifetz's sound is its vintage passion and collimated fury. One listens to Heifetz to expand one's soul.
