It's still not the same thing. Even with the gadgetry that even lower end cars have nowadays, people still have an interest in high end ones of various sorts that lack that gadgetry.
Lower end cars with gadgetry are still just vehicles, serving no different purposes from higher end cars. Also many higher end cars can still be equipped with much gadgetry if needed. That's not the case with watches.
As a parallel you have watches that might lack gadgetry, but are solid in territories where you can't use such a gadget, like deep in the sea (Rolex Deepsea) or out in space (Omega Speedmaster Professional).
Of course, which is why we still have featurephones in use and those special purpose watches will remain. However that does not mean the watchmakers will face decline if smart watches become the norm. Just like how most SUVs aren't used for "sports", I suspect much of the sales of such watches are made to people who buy them for other reasons.
And that's leaving aside the myriad who buy such things to show off and won't replace them with something cheaper.
I doubt there will be too many of them, assuming, again, Apple and others will find a way to make smartwatches really useful. Nobody like showing off diamond encrusted featurephones because people actually like using smartphones and using a smartphone has become a habit for so many.