I think there is probably a way to make a fun, Age-style RTS with dropsites. But I personally don't think AOK was that game. In AOK, you made a few dropsites early, but later on all you did was spam TCs everywhere -- they were cheap, they could gather any resource, they could shoot, train villagers and be garrisoned.
If you really had to build Storage Pits, Granaries, Lumber Yards or whatever throughout the game, I can see why there would be either some interesting choices or player skill involved in building them.
But in AOK, players quickly found the optimal placement for their food and gold dropsites, made a few lumber sites, and then just went TCs all the way. Even Farms were serviced by TCs. Dropsites were pretty much a non-feature by Age3 in AOK and AOM. If you really thought placing those first few dropsites in Age1 and Age2 were really fun, I guess I could be convinced of that, but at that same point in AOE3 you have a lot of other things you need to manage. Once you get past that point, the economy is largely on autopilot in all of our games.