I was going to agree with Sylvester that your argument in the OP depends on jhana and samadhi being equivalent, which I’m not so sure is that case. I’d tend to think that samma samadhi is some degree of unification of mind, with “samma” requiring that the other 7 path factors are present (though mastery of samadhi would seem to more solidly equate to jhana). IMO it’s a subset relationship: jhana is a subset of samadhi, but the contention that the subset relationship goes the other way is more shaky.
But your second post is interesting in that it seems to actually have a jhana reference. If so, that’s an interesting data point!
The first jhana seems to be more often described as “born of seclusion” rather than “born of concentration” (as for all the others), so if your theory did actually hold, I guess it is most likely to do so in the first jhana. If ekagatta doesn’t hold for the first jhana (though other suttas go in the other direction), this puts less restrictions on the possible meanings of vicara vitakka. Though there’s still, even then, SN 36.11 constraining their meanings. According to that sutta, speech ceases in the first jhana (more on that later).
To go off on a somewhat related tangent, lately, after reading a sutta with mention of the three formations: verbal, bodily and mental, it struck me that successive cessation of these is really what is supposed to be happening in jhana. This would tie in with the cessation of speech in the first jhana as described in SN 36.11, the cessation of breathing in the fourth jhana (surely, that’s the body close to shutting down) and the cessation of feeling and perception (surely, the mental formation has ceased at that stage). You’ve probably thought about all this before, but anyway, I’ll go on! 
The cessations of the three formations are also described:
“Then, bhikkhu, I have also taught the successive subsiding of formations. For one who has attained the first jhana speech has subsided…. For one who has attained the cessation of perception and feeling, perception and feeling have subsided.
MN 44 has some very interesting things to say on this topic (Bhikkhu Bodhi translation):
(FORMATIONS)
13. “Lady, how many formations are there?”
“There are these three formations, friend Visakha: the bodily formation, the verbal formation, and the mental formation.”
14. “But, lady, what is the bodily formation? What is the verbal formation? What is the mental formation?”
“In-breathing and out-breathing, friend Visakha, are the bodily formation; applied thought and sustained thought are the verbal formation; perception and feeling are the mental formation.”
15. “But, lady, why are in-breathing and out-breathing the bodily formation? Why are applied thought and sustained thought the verbal formation? Why are perception and feeling the mental formation?”
“Friend Visakha, in-breathing and out-breathing are bodily, these are states bound up with the body; that is why in-breathing and out-breathing are the bodily formation. First one applies thought and sustains thought, and subsequently one breaks out into speech; that is why applied thought and sustained thought are the verbal formation. Perception and feeling are mental, these are states bound up with the mind; that is why perception and feeling are the mental formation.”
There’s a bit more later in the sutta about how, on the way to attaining cessation of feeling and perception, the speech formation ceases first, then the bodily and then finally the mental formation. Analayo says that, while the Chinese parallel to MN 44 doesn’t really have this part about the formations, a Tibetan parallel closely mirrors it (though the mental formation is equated to “perception and intention” rather than “perception and feeling”).
Equating the speech formation to vicara vitakka is quite neat. That nicely explains the description elsewhere of the second jhana as being “noble silence”.
But what is a little confusing then is that SN 36.11 has speech itself ceasing in the first jhana, while the MN 44 has the speech formation ceasing in the second jhana. Evidently there’s a difference (either that or one of the suttas is confused). I suppose the sentence:
"First one applies thought and sustains thought, and subsequently one breaks out into speech; that is why applied thought and sustained thought are the verbal formation.
does point to vicara vitakka as being the underlying basis for speech (what can cause it to form). Perhaps speech itself is the first to be suppressed, and only the speech formation itself in the next jhana.
I suppose something similar may happen at the fourth jhana. In several places in the suttas, it says that breathing stops at the fourth jhana. I guess, though, that one really only has fully gone beyond the body in the arupa jhanas, i.e. perhaps actual cessation of the body formation only happens there.
Does something similar happen at the base of neither-perception-nor-nonperception? Presumably, there is not much left in the way of feeling or perception at that point, but maybe the mental formation itself only fully ceases at the stage of the cessation of feeling and perception?
I suppose this line of thought is fairly concordant with AN 10.72 (the Thorns suttas perennially coming up in these jhana discussions ):
"To one who wants seclusion, company is a thorn. To one developing the sign of loathsomeness, an agreeable sign is a thorn. To one protected in the mental faculties, sight seeing is a thorn. To a man leading a celebate life, the behavior of a woman is a torn. To one in the first jhana, sounds are a thorn. To one in the second jhana, thinking and examining are a thorn. To one in the third jhana, piti is a thorn. To one in the fourth jhana, in breathing and out breathing is a thorn. To one attaining the cessation of perceptions and feelings, perceptions and feelings are a thorn. Greed is a thorn. Hate is a thorn and delusion is a thorn.
The thing one has just quietened to get into a particular jhana also tends to be a thorn to that state. Second jhana has suppressed vicara vitakka and so that is a thorn to that state, the same for breathing to the fourth jhana (I guess the relevant formation hasn’t fully ceased if the associated thorn can still knock one out of it). It’s interesting that sound is a thorn to the first jhana. If speech rather than the speech formation is what is suppressed in the first jhana, does this mean speech and sound are essentially the same thing here?
If the speech formation is a thorn to the second jhana, could it similarly be said that speech itself (or perhaps equivalently sound) is a thorn to the first jhana? Perhaps a possible reason for sound being a thorn is that it also may tend to stir up speech in the mind?
This all runs a bit counter to the hypothesis of your OP, but seemed relevant anyway.