CK3:
- 95% of characters can't do anything about tech.
- The 5% of characters that can choose their tech still can't meaningfully affect the tech rate beyond getting the first bonus in scholar lifestyle.
- Average development is impossible to meaningfully affect unless you do gamey strats like limiting culture spread, which is the opposite of what the goal of the game should be (everyone wanted to spread their culture).
- If you tech too quickly you end up hitting arbitrary date roadblocks that stop you from advancing to the next era.
- Regional techs are pretty cool.
CK2:
- Every Duke can generate their own tech points
- You can tech to anything, at any time
- No limit to how quickly you can accrue tech points, unlike CK3 where fascination is capped at 100%. Make a 50 learning god? You can get a lot out of that. You could also get tech points from other stats than learning.
- No era date limits on tech, if you want something sooner you just need to pay the ahead of time cost, which is a strategic decision.
- Probably the worst part about CK2 was the whole spread system, which was painfully slow.
It can be noted that both games had the issue of "just move your capital to a high tech area and you gain all of their tech"