It's entirely possible that they're being honest on that.
No, it's not. For starters, they already had Sync which did pretty much the same thing, sans monetized data mining, without having to integrate a 3rd party service with an intrusive privacy policy into the core browser.
That privacy policy should qualify as a "serious prohibitive quality" and the fact that you think it doesn't makes me question your honesty on the subject.
And first the claim was "user feedback" -- the mozilla feedback page shows that's clearly not true (the feedback, last time I looked, was unfavorable at a 9:1 ratio), then it was "popularity", which is still BS - As has been pointed out, it has about ~1% of the popularity just of ABP, which would put it, as a percentage of the whole, at around epsilon.
Not to mention the fact that several extensions intended to un-fuck the UI have been twice as popular or more, but we don't see them worrying about the popularity there... that position is still "up yours, install an add-on if you don't like our brilliant UX".
About the only way that hard-coding Pocket into the browser is not mind-numbingly, earth-shattering incompetence is if they got paid to do it. I mean, we're talking the no business near source code, drooling on the keyboard, typing by hitting the keyboard with a squeaky mallet kind of moronic.