Not everyone codes and creates on a MacBook. This is where Tims understanding comes into question.
No they do not, which is why we're going to be seeing a new iMac now that the appropriate CPUs are shipping from Intel and the appropriate GPUs from AMD.
As for the Mac Mini, I don't see it as being something an iOS developer would use. Maybe back in the early days of iOS and the App Store as it was an inexpensive way for Windows developers to get into Apple development ecosystem, but today they're almost certainly using MacBook Pros and iMacs. Which is why I believe the Mac Mini is a dead product line.
The Mac Pro is a bit more complicated, IMO. I think the machine is probably overkill for most iOS developers, but I know there are large and successful iOS developers who do use Mac Pros for that work (though I expect not exclusively and they bought the Mac Pro for it's prowess at other tasks first and are leveraging it for iOS development second).
I more and more believe the current Mac Pro design was a major failure from a technical and/or sales standpoint - much like the Mac Cube was. Such an opinion is pure speculation with no evidence, but that it has sat still for so long makes me think that something is "wrong" with it.
Because you have to buy it with two GPUs whether you need them or not, it's very expensive. So many who bought the old Mac Pro are instead buying the iMac (especially the 5K iMac). We know you can upgrade the CPUs to newer generations of Xeons that use the same socket, but perhaps the GPUs are much more difficult to design upgrades for (and you have to buy two of them, which would make such upgrades very expensive).
There have been rumors that Apple has been looking into moving production from the USA to China and you do that either to improve production scale (which is likely not an issue) or reduce production cost (which likely is an issue). So maybe the current design is too expensive to make, even with what Apple charges for it.
Apple crams a lot of high-temperature components into a compact case with the Mac Pro, so perhaps it has a high failure rate which results in a very high repair cost (higher than what AppleCare and it's own margins can support).
If Apple has lost significant money on this Mac Pro (in the hundreds of millions of dollars), they're not going to be very interested in spending even more on it. And Apple is loathe to admit design mistakes, so the chances of them going back to the old "cheesegrater" design is not going to happen.
Which means if Apple is planning a new Mac Pro, it may very well be a new design and that could be taking years to engineer - especially if they still want it "compact" but more upgradeable and reliable than the current design.
Or it might also mean Apple is done with the Mac Pro after this failed and expensive experiment.