I agree with alf5071h that my "normal" is not the same as everyone else's "normal". However, the 744 is EXTREMELY stable, capable, and well-behaved on wet runways. I still suggest that if a 744 has a problem stopping in its 'normal' distance, any other airplane will have similar problems or worse.
However, I do NOT assess braking action "from the apparent deceleration". I assess it from the amount of antiskid release action (i.e., the "deep skid" he describes) I can sense through the brake pedals as well as any yawing tendency from asymmetric braking/releases.
I am very much a "seat of the pants" pilot (from my old glider and Navy carrier days, and more recent Champ time) despite 17 years of 747 flying. I have a good sense of what is "normal" on landing roll in the various configurations of Flap, Autobrake, and Reverser. I am also aware of the relationship of the input of Runway Condition into the performance calculations, and the Autobrake setting at which there will be no further landing roll reduction when using only Idle Reverse. From those inputs, I believe I can give a reasonably accurate assessment of actual Runway Braking Action.
I also realize that every airplane will respond differently, and any 5 pilots may give 3 different Braking Action assessments. That's why ATC gives the time and airplane type when reporting those PIREPs. It takes little brain power to assess consistent reports, but a bit more experienced-based translation to assess a handful of differing reports. If the information is available, it will still serve to warn and assist the following pilots.