It seems that every technology that has a successor gets more expensive and takes longer to research in the next age. This makes sense because in theory you have a better economy in the next age to afford more expensive things and better upgrades can snowball quickly so you need to increase research time so the game can be more balanced.
One exception is wheelbarrow and handcart. Wheelbarrow (feudal age) takes 75 seconds while handcart (castle age) only takes 55 seconds. Why isn’t it the opposite? It would make sense to have wheelbarrow shorter because you only have 1 town center to produce villagers and make handcart longer to compensate for the ability to make villagers out of multiple town centers.
Also this would nerf vikings slightly because you wouldn’t be penalized as much for researching wheelbarrow in feudal and making handcart longer wouldn’t be as punishing since you could in theory keep making villagers out of other TCs. The devs could lower the UT chieftains cost back to where it was before the anniversary patch. I think increasing chieftains price wasn’t the best way to nerf the vikings anyway.