Indeed.
Terms and definitions exist only as a shorthand to avoid having to describe every single thing from scratch. They're there to be useful and convenient. Start chasing the limits of them too much and they stop being that.
To be clear, I'll state from the outset that I agree with the gist of what you say.
"Terms" and "definitions" are literally (in their original Latin at least) "drawing lines to mark limits, ends". They are just words though, not descriptions, so they cannot possibly contain all that is and happens. OTOH they determine, or influence, depending on what version of linguistic relativity one defends, the way individuals categorise objects in their mind.
It's not the only factor though. Prejudices of various kinds also have their say in what differentiates snow from slush, azure from aqua, bass from guitar to one's eye. Case in point, a lot of players here and elsewhere clearly are negatively obsessed about all things guitar, and make every effort to have them and their instrument of choice be told apart from everything remotely related with the 6-string Spanish-tuned annoying little imp. "I play electric bass, not bass guitar; my instrument has evolved from the upright bass, not guitar; don't use a pick; don't play chords; avoid anything other than all-fourths tuning; if you want a six-string why don't you just play guitar?" I could go on. Overcompensators? Closet guitarists? The real, true failed guitarists? I don't know, I just play (and eat e-popcorn on TB).
"Bass guitar" and "guitar" are two points in a continuum, or, rather, overlapping segments of a straight line, or, perhaps more aptly, dialects of a language. They don't exist as razor-cut, self-evident categories per se, they're only defined by a set of dialectal features more or less arbitrarily chosen: the isoglosses of said features sometimes cut the map at around the same places, often not.
Let's take the bass VI (not the model but its ilk in general): tuned E to E, ultra-narrow spacing, 30" scale, guitar pickups, guitar hardware. Is it a guitar? Too long and wrong register. (Pernickety? Maybe. And maybe those two are pretty egregious points actually.) Is it a bass? Naaah, per the above, many could and do say. And yet, the spacing is the only thing inherently un-bassy about them: there are instruments with one or more of those features that are easily recognised and agreed upon being called basses. Abraham Laboriel's long-scale sixes (same tuning); Beatle basses anyone? They're shorties, with guitar tuners. Broncos? They're short scalers too, and have a Strat pickup, six polepieces and all.
Thin gauge? I can put as fat a bridge-cable E as I want on my VI, and use extra-light strings on my 34", and still have them sound like a bass in both cases.
And then, perhaps, "bass" is an intersection of "normal" features, or a set of weak constraints: one can violate one of them, or one other, or a couple, but go astray in too many directions and folks will resist using the label. Piccolo is OK, to many, on condition that it's 4 strings and wide spacing and no shorter than 30 inches; many strings are still OK, but make the lowest string an E1 at the highest; and so on. I'm just attempting an explanation, not being prescriptive. I tend to use terms liberally and incusively myself, and look at intent and function.
In case anyone wonders, the reasoning in the wall of text above is called nominalism. And by the way, please y'all: consider cutting the "semantics" cr@p, will ya? Semantics is a science (look it up), not pointless quibbling about shades of meaning instead of pursuing action, or getting to the point, or simply agreeing with the guy who cries "Semantics!" first. ("NEEEEERRRRDS!!") But I guess there are less semanticians than there are physicists to point out when a word carelessly thrown in enough times has become an empty buzzword. As in "it's just physics, man".