Reading this discussion about tanks, I'm thinking back to one of the DDs for East vs West. Remember how you were supposed to be able to design your own warships? What if you had an option to do that for your tanks in HOI4? Such as choosing whether to favor armor over speed. Nothing absurd (like choosing the type of suspension), but it would be so that technology alone isn't the sole factor in whether your tanks are decent or not. Plus, for role-players, you could design tanks in a historical manner (such as making German tanks expensive, but overall quite good.)
This
does come at the risk of increased micromanagement, something that the devs are trying to cut back on, but perhaps the system here would be that, by default, each tech level gives the same quality of unit to every nation, but you (and the AI, if it's smart enough) are given the option to make changes to the design before putting it into production, such as adding more armor at the cost of slower speed and reduced toughness (reliability). So, you could have British and German tanks identical on a technological basis in 1941, but Germans could choose to prioritize speed over armor and armament (or, alternately, do the opposite). No railroading, no excessive micromanagement, and best of all, it's optional.
But, this being a Paradox game, I'm sure there's a glaring flaw somewhere in this proposal that I didn't manage to spot