Conclusion: A RTS game where your main opponent is the map your building on.
To design an RTS knowing what it is helps quite a bit. According to Attempting to define the RTS Genre. There are a few key components that define a RTS outside of the obvious need for some sort of real-time element. Economics of some sort, a competitive element, multitasking and an uncertainty of player’s actions via fog of war for example. Another key point they bring is up is the fact that any invested resource can be lost this is key to the game we’re about to design.
Starcraft 2 + Warlock Arena map from Warcraft 3/Dota 2. Putting in the map of warlock with the edges falling off ticks off a lot of the boxes for what I want this RTS to be. The choice of whether or not to ‘farm’ the unsafe but high yield resource near the edges always aware of the risk . Having an AI along side you fighting for the same finite resource could add to the heftiness and uncertainty to every decision made by a player, Invest in destroying them or survival? Even without an AI opponent having the map react to what is built (heavier building may drop faster?) could simplify this whole premise but still achieve all elements of a fast paced and hopefully fun mini RTS.