When it comes to feel *on track*, I suspect it mostly has to do with pushing the pedal and not getting the expected response (slowing down with increased pressure). So because you are pressing harder and harder with no result, to you it "feels" soft. Same thing happens when pads glaze over. As long as the fluid isn't boiling, you're not generating any less pressure in the lines. You're pushing the brake pedal further than you anticipate needing to do so to get the desired response... your mind interprets this as a soft pedal initially.
A great example on my last car was switching from Hawk HPS 5.0 pads (which are excellent daily + autocross pads IMO... they dust a bit but it's easy to clean, they're quiet, etc) to G-Loc R12s. Any one of those compounds gives you so much more bite earlier in the pedal travel, that instinctively it seems firmer when in actual use. Just sitting still and pumping the pedal though, there is negligible difference between the two pads. I may or may not have blown about 10ft past a stop sign once after swapping back to street pads and forgetting how much less grabby they are