pretty sure asf are quite a bit more mass efficient than if you account for the hp discretization advantage. They are pretty much on par with inties when you look at hp*dps/mass².
one nice thing about swifties is that they are quite cheap in power. About the level of inties if you look at combat strength.
@Arran for those efficiency calculations maybe you want to read this:
Unfortunately I did never finish it and it isn't a nice read and I still have an error in with the variables from point 2.5 on. Which is probably for you the more interesting equation because it takes the advantage a unit has due to its higher overall strength into account. Also I am quite sure these calculations have been done before but I didn't read anything up so therefore no references.
But as stated it is not really possible to count smth imba just because of doing some calculations with stats if gameplay testing claimes it is balanced.
These balance calculations only help with getting a good initial base line for balance and isn't really good enough for finding errors within.
It is comparable with walking into the engine developement section of mercedes benz and start talking about the ideal gas equation.