Cook doesn't seem to a have any taste for product design, isn't he a logistics guy?

I don't think that's fully accurate, unless you have a link that confirms it? That Dye designed it, I mean, not that it was horrible...

Jony Ive was the head of design at that point (both hardware and UI). Wikipedia says Dye "contributed greatly to the design language of iOS 7" but Ive would have had final say. Certainly at the time as I recall it, iOS 7 was seen as Ive's baby.

Also, I'm not defending iOS 7, but I reckon its visual design was a lot more influential than it gets credit for. Think of those ubiquitous Prime bottles, with their bright saturated color gradients; the first place I remember seeing that style was iOS 7. I bet they picked that style for Prime because kids liked it, and kids liked it because kids like iPhones.

Edit to add: "bright saturated colors" goes back a long way to Fisher Price toys and the like, of course, but it's the gradients specifically that I think iOS 7 popularized.