I didn't participate in the poll because my answer isn't really offered in the options.
I think the idea that you need to stick with one instrument is one held by people with 1) one personal "voice" on the instrument; and 2) super chops. It's largely a jazz sensibility.
At one point, back in the '80s (I think), Pat Metheny was still playing the very same guitar that he'd begun playing on. In some interview, Jaco said that he used only a Jazz Bass because "It's the one I know." Billy Sheehan is another one. When I saw him in concert several years ago, he had been endorsing Yamaha for quite awhile, but was still using his same old battered Fender onstage.
These are people who developed a personal sound, and are (or were, in Jaco's case) incredibly fluent largely because they'd played one particular instrument so much that it became like an appendage.
There are others who need to sound different in different situations. I remember the Bass Player article years ago featuring top country session bassists; each one brought about 10 different basses to each session-- 4-string, 5-string, fretless, active, passive, flatwound strings, roundwound strings, old, new, etc., etc. For these people, versatility is the main need, more than superhuman fluency, or one identifiable sound.