Nope, tack is sometimes used to express "taking a direction", it has it's roots in sailing terminology.
It was also a play on words on my part, given the the story of the naming of Jolla/Sailfish, & the fact that participants in that movement often refer to themselves as "Sailors".

So you're making the assertion that it has to automatically be a bad thing based on; other co's, which are fully established, are (comparatively) massive, who's paths/stories are completely different, & for which it's yet to YTBFD* whether they're going down directly thanks to changing one or more CEO's too quickly? No offence, but I think the whole argument is quite strange, co's go down for a whole range of factors, yes CEO's are usually the single-biggest factor, but often it's far more complex than changing 1 or more CEO's too quickly. Even looking at CEO's & their actions only isn't always the full story, especially for larger organisations, but it's definitely more significant than rate of change.

And you're framing the argument as though pointing out case history is the only way towards some kind of "truth"...
Read the articles I referenced (no time to find them ATM sorry), they've explained the basis of their approach**, it's based on a text-book analysis of how one supposedly runs a agile start-up, whether or not it's the "best" approach I've no idea, I'm no expert in the area. I've no time to dig up "case histories" of start-up's using such an approach, but I'm sure if one were to expend some time it'd be possible, & I'm sure there's several very different arguments "for" & against" such an approach.

I don't see how it's a good or bad thing, there's simply not not enough info on the internal machinations, plus nothing has happened on the actual market in order to determine where the mistakes are being made or (more typically) "were made", that'll come soon, & there'll be MANY. I'm all for criticising tangible things, see many of my earlier posts. *DISCLAIMER* I'm probably always going to be a backer, even if the final 1st product "isn't enough", mainly because I want to see at least one more "Android" doing well on the worldwide market, & so far I only see Sailfish as being closest to that.*** But that doesn't mean I'll hold back on attacking real problems where I see them, doing that will only hurt what I'd like to see happen.

*for most (if not all) of the examples you cited
**aside from explaining the basis for their relatively regular movement of people, they've also explained each specific change in detail
***for reasons I've mostly outlined in older posts, the other contenders sit further back in my interest queue