I am not surprised by your experiences. And before I put forward my theories I have to say it is an utterly subjective argument because tyre choice and suspension has an enormous effect on braking performance.
If you check my post I hope it was clear that i proposed that great brakes on the front with standard rears will only increase understeer. As previously stated this characteristic, however, will also be affected by tyre choice ( both front and rear) and suspension settings ( spring rates and damper settings/choice). Understeer is by far the safest characteristic but excessive understeer makes a car horrible to drive.
However, if you are hammering along a straight road and a child runs out then what you want is a balanced braking system. All four tyres sharing the stopping forces more or less equally.
Out of balance brakes may just be the difference between a dead or a live child.
Great front brakes will lock and skid more easily and ABS will kick in earlier and be required more. Skidding front wheels, even under the control of ABS, will not be as efficient as rotating tyres that are being controlled by the brakes. This will put more reliance on rear brakes. With a balanced brake set up all four wheels will share in the braking process, which i believe must give a quicker stopping time.
Great front brakes alone will just put the wheels into a locked situation more quickly.
I think a straight line brake test is the only way to prove this either way. Clearly my opinion would need to be proven. Let's call top gear and set it up!
As far as your braking system is concerned, the brembo calipers will make little difference ( maybe slightly more cylinder surface area and therefore slightly more braking forces,)
The braided hoses will give absolutely no improvement in braking performance.
And finally a well bled system with new fluid is no more than expected as standard.
The DS2500 pads are rated for track day use, i believe, and ought to create an improvement over the original brakes once hot, though perhaps not so much in 'normal' road use. Also, the change in performance depends on what pads you were replacing in the first place.
My Spider currently has really good brakes. I demonstrated them to my mate by braking from 130mph down to a stop. His face nearly fell off. As I do not know the pads I have now I am slightly concerned that I do not destroy the great brakes I currently have by trying to "improve" them.
The GTV and Spider both have understeer as their basic handling characteristic, even more so with the V6 models. Perhaps the slightly better front brakes does not alter this basic characteristic by much in normal driving. I contend, however, that anyone racing a car would ALWAYS upgrade both front and rear brakes simultaneously. To maintain the front rear balance. QED, I think.
My driving style is firmly in the "slow in quick out" camp and most of my spirited driving consists of braking in a straight line and powering through the bend. I find that the spider does not respond well to a dab of brakes mid-bend and thankfully I think most of us never get to find out how much worse it could handle when the fronts are uprated whilst the rears are sacrificed.
I enjoy the debate and look forward to your response. You are probably right in what you say. For normal quick road use the change in brake balance is so small that it is virtually insignificant for most of us. Especially as we go slow in and quick out.