I'm generally inclined to believe that companies--and people--aren't lying outright, unless there's evidence to the contrary. Apple seems to be making a real, concerted, and good faith effort in the realm of data privacy. This effort ought to be recognized.
Would it be _better_ if all Apple software was fully open source and could be independently audited by anyone? Yes. Does that invalidate everything else? No.
Also, Wireshark is a good way to monitor what data your phone is sending to what servers, even if it's incredibly imperfect.
With ubiquitous use of TLS and the advent of certificate pinning Wireshark is becoming less and less useful. Even if you convince the phone to accept your man-in-the-middle certificate with a provisioning profile, there's no way to proof that it sends the same data as if it got the real certificate.
If iOS was changing the data it sent out depending on which root certificates were installed, that would be a huge scandal, as I cannot imagine _any_ non-malicious reason to do that.
That's not proof of anything, but again, at some point I feel you have to assume good faith. Apple does not have a history of doing stuff like this.
Would it be _better_ if all Apple software was fully open source and could be independently audited by anyone? Yes. Does that invalidate everything else? No.
Also, Wireshark is a good way to monitor what data your phone is sending to what servers, even if it's incredibly imperfect.