I'm not sure that's a great comparison: four years would seem about right, given PA Semi's main expertise at the time of acquisition was Power rather than ARM. Designing a custom ARM core isn't rocket science, but it's pretty close: plus you've then got to actually get the things fabricated at sufficient yield.

I am not sure they could have done things much quicker to be honest.

If you think mapping and cartography are much easier, you've never given that a shot, it's a can of worms.

If i recall correctly, PA Semi's founder(s?) were from the DEC StrongARM team - so there might have been some prior experience.