The SF/Inf/Archer thing is mainly just one of cost and utility. SF cost a tonne up front, but are cheap as cheaps in weekly payment. Inf/Archers don't cost that much upfront, but often cost 2-3x as much per week. They do have the advantage in takeovers and civil work though (AFAIK), just due to the number of bodies working.
#normal_troops*0.18*other stuff compared to #SF_troops*0.18*1.75*other stuff sounds pricey for the SF, but it evens out nicely due to having about 1/3rd as many of them.
Also, don't forget repair times. With 165 infantry, it takes an entire turn to repair 10% armour. And move times. Bigger units take longer :/
These are pretty good at shredding rogues:
Mixed Infantry 55 85 / 55 (quite unusual to see good Mixed infantry)
And these aren't too bad:
Emerald Sabres Infantry 60 90 / 70
