In real life when a NEW technology is researched, it bring about new way of doing things and major chances. The technology will get polished and improved. However, it will come a time when improvement to this technology is more and more difficult. A clever man come along and come up with a new way of doing thing or see thing in a different angle, and we got a technology breakthru, and the cycle repeat.

I'm suggesting to represent the above with minor and major reseach level, just like software version.

A tech start off with version 1 (version 0 means unknown tech)

When it is researched, it get minor improvement over time i.e. Sword 1.0 to Sword 1.1 etc.

Minor version get high % improvement on the base value initially but drop significantly when the minor version goes up.

i.e version X.9 will get less improvement over X.1. However, a higher minor version will give a better chance of getting a Major improvement. Which symbolised a major technology break thru that give a hugh improvement on the base value. and the cycle repeat.

Major tech version is not researched, it happened by chance. Certain Heroes (tech based/scientist type) have special skill that improved the chance of getting a major improvement.