Stiff front will only make it understeer more. Stiffer rear is the way to go. Put some chocks between the coils on the rear and test. I make up some blocks to go between the coils, put some holes in for big zip ties to hold in place and do a short test.
The rates for the rally car would be for dirt and have to do with long travel and stopping bottoming out. I have a mate/old boss that has been works driver and international navigator and is also a major race tire distributor whom runs an ex works Daihatsu with his son-in-law on dirt and asphalt - prompt me to ask some questions of him.
If you stiffen the front it is only going to transfer more grip to the rear. Add the sway bar when you get the rear rate correct and make sure it is the smallest bar you can get away with, it should have three or four adjustment settings on the blades (as in holes to change the stays). This way you have a way to tune the car on track days by using the holes or even omitting the bar (if it is a big bar then disconcerting will have too dramatic of an effect).
Stiffening the front not only makes for understeer but if you have an open diff you will have a lot more wheel spin. Do you have an lsd?
Play with one end at a time or else you will confuse yourself. Again I say stiffen the rear first with chocks before buying springs front or rear.
Based on your pics I’d say the 205 has less steering angle and is either taking a way diff line or is only just turning in and weight has not transferred. Pic is not good comparison.