maybe it's because in a first person shooter you have to process the actions of each unit individually, where in a strategy game it has to process the behavior of an AI controlling all those units
Humans are a lot slower than AI. First person shooters are pretty simple. You have, on screen, maybe a half dozen units whose input comes in from players at around 1 command every 100ms.
What makes strategy game performance hard is the CPU. The game has to manage the entire map (so it's both client and server), all the units, all the cities, etc. every frame.
In terms of performance, 1.4 should be much better as it does a lot more with things that are off-screen (i.e. reduces what they are doing).
If you have a lower-end CPU, you may want to try smaller maps (fewer things to keep track of). You can also turn off outlines if it's a GPU issue as it's expensive.