For the most part, I agree with the OP. The constant struggle over the Triforce seems to be hindering Hyrule's technological growth. When they're not busy fighting each other over the triforce, it seems that they do have a period of technological growth-that is, until some sort of evil plagues the land in search of the triforce, destroying everything and halting progress.
I'd also like to point out that technology in Zelda seems to be more or less divinely or spiritually inspired, as opposed to just being created for the sole purpose of making life easier.
The robots of SS, as well as the trains of ST have direct links to dieties or some sort of spiritual conflict in the past. The robots are implied to have been created by either Hylia or Lanayru, and due to this, directly serve them, as opposed to humans, which they don't seem particularly fond of. The railroad system of ST was created by the spirits of good as a seal to lock away Malladus, and overtime, came to be used for trains, which in turn seem to have their origins in the spirits of good as well.
The technology of the Oocca may have been inspired by the gods as well, as they are said to have been the closest race to the gods.
It seems as though the humans just take advantage of the technology, rather than creating it themselves. Even if they did create something, there is more than enough evidence to suggest that it was reverse engineered and modified from previously existing technologies.
/\ presumably they have. However, no one but Anouki or yetis would live in the new Hyrule plateau in the CT/DT, as it is far too cold (preposterous altitude, possibly beyond the Powico arctic circle etc).
But yeah, the advances shown in TP are an example (IMO) of how slowly the populace are progressing in the other two timelines, but are progressing nonetheless.
I agree that the constant threat of Ganondorf impedes the advance of technology, but there still seems to be some advances outside of the Adult timeline.
TP has mining equipment, several places in the Downfall timeline have rail tracks.
The towns however always seem low tech no matter what the timeline. In spite of having Spirit Tracks no settlement in New Hyrule seems particularly advanced.
For that matter how do we know the Locomo haven't created the tracks to bind Malladus in the other timelines?
Well, theres no doubt that the other races are advancing, but are there any examples of advancement in human technology? I know there's a camera in Wind Waker, and a jukebox in Ocarina of Time(Bombchu Bowling Alley is the only place to have one), but I can't think of anything else right now...