Well...
It doesn't quite work like that...
As has already been mentioned ...the different kinds of closed source there is in the two examples of Android and Sail..
Android uses closed source apps.
Sail uses closed source UI...

(and it would be great if someone here did the legwork ...and did a list of exactly what all the various os's closed source aspects were...so as to compare.)

So back to the example...
Which is more dangerous and more compromising to have?
Black boxes in apps?
Or
Black boxes in the UI?

From where I stand...my perspective is that I can use alternate open un-compromise-able apps far more readily than use an alternate UI .

If at any point the UI becomes abused or compromised...it is truly devastating.....since everybody uses the same UI

One can easily migrate to open, secure and safe apps easily enough...(and at worst do without a couple ...say in the result of a perceived threat or threats..)
But ..migrating to a different UI so easily if it becomes compromised or abused by those who control it? Not easy.
And we have seen from the past, any organization or corporation that say they have everything under control, and everyone's security and safety in mind, end up becoming compromised by either flaws, that go unreported and kept hidden from the public (in some cases for years...leaving everyone except the corp.vulnerable and unknowing of their compromised security...
or ..
it becomes compromised by the "State" where the corps. resides...or by a foreign State...
done under the premise of "national security".

That is why I do not use apple phones.
That is why I did not use MS phones.
That is why I won't use Sailfish . (and yes a LONGGGG time ago I wished they hadn't diverged into what Sailfish is now..and just kept up with MER and Nemo...loved old MER especially...)

For all the dislike I have for android ...(which is really a dislike for the app market mess it is...and having to cherry pick apps)
it is a safer option in the current climate ...in my humble estimation.

(of course I do love my buntu phone ...won't forget that mention...
and hope for the best for Leste and its advancements...and I really should check in on Plasma Mobile again and see how they are doing ...its been a while.)