For the love of all that is holy, I beg you to reconsider this mechanic. If there is no major rework of it planned in the next few years, then please at least consider a small update.
For example (and I am not saying this is the exact way development should work), development could have 20 levels, and the efficiency of buildings in a county could scale more noticeably with higher development. A building in a county with 20 development could be, for instance, 10 times more effective than one with just 1 development.
I do not know how hard this would be to implement from a coding perspective. I am just putting this out there as feedback. Right now, development feels way too underwhelming and does not really serve its purpose of representing population or urbanization properly.
Hopefully, a bigger economic overhaul is on your roadmap for the next 2 to 3 years, and development will get reworked then. But if it is not, please consider at least adjusting the numbers behind it. That kind of change should not take a huge amount of development time, would not require new mechanics or art assets, and could make development a lot more meaningful and realistic — or at least that is how it seems to me.