Since the game went through multiple expansion cycles without a movement arising for the removal of the deferred promotions, I think we can consider the design decision reasonably sound. Compare to the chop, or insta-heals in Civ 5.
There is nothing inherently evil about deferred promotions. They produce a simple tactical choice: suffer more damage now in order to keep options open, or expend the resource in return for an immediate bonus.
Fixed it for you. What you describe is micro. It's bad game design. There are reasons I swiftly uninstalled Civ 3 and booted up SMAC if I felt the urge during that time period. That mechanic is one of them.
That may be the intent, but the problem is that it is not the effect. The optimal response to this set of changes is to engage in precisely the sort of behaviors you disdained in Civ 3. Optimal play will require micro of XP gain and Culture gain. The latter is particularly problematic. Think about it: the intended check on horizontal growth is the Culture system. As you settle more cities, you gain fewer SPs. But several later SPs are strictly better than earlier ones, and costs scale, so the change creates the perverse incentive to encourage horizontal growth and early Culture avoidance in order to defer SP acquisition.