Hi Irvine
You've spotted the central assumption. Actually the axis of rotation during a casting stroke is far more complex than you might think. It's unlikely to actually be anywhere along the length of the rod - the rod is at one the end of the arm which is flexing at the wrist, elbow and shoulder - so the actual axis of rotation during a stroke is probably below the end of the rod, depending on the style it may also be behind the rod... it can even move during a stroke. We also don't deal with the bend of the rod during a stroke.
We wanted a means of measuring rods of approximating the MOI so for that purpose placed the axis at the butt. Thing is, it makes it more intuitively obvious that if the mass anywhere along the rod in increased the MOI increases - so while fitting a heavier reel may place the centre of balance under the hand it actually makes it more difficult to rotate the rod - that's apply angular acceleration, speed-up
and stopping force. (At this point I was about to suggest you think of a tightrope walker - holding a long heavy pole - they hold it at the middle and its the weight away from the middle that gives them stability - if this was Sexyloops that would lead to weeks of argument
You're right to question the caster's sensitivity. You might be surprised how sensitive we are when physically comparing quite similar rods, switching back and forth between rods, a decent caster can discern a difference of a few gm^2.
The weight of the line is the weight of the line
so to speak. If I cast an S4 and an S3, same length 9ft and lineweight #5, with the same line why do the outfits feel different? Well one reason is the swingweights of those rods is different - 74.7 and 61.4 - those figures are specific to the rods measured but give a clear indication how Scott changed things and by what order of magnitude when they introduced the S4. The effect of that reduction in swingweight is that it is easier for me to accelerate and slow down the S4 - imho the effect is possibly more noticeable for short and medium casting distances - when I'm using smaller weaker muscles and trying to make small accurate rod movements. Try making a delicate mend using wrist alone - with a very heavy rod then a very light rod.
On the issue of the line, we work against both weight, meaning inertia, and drag or air friction - with a fixed length of line the inertia remains constant whatever the rate of acceleration the drag factor increases exponentially with velocity. The same is true of drag forces on the rod. So a fat rod feels different to a thin one. If you think we're not sensitive enough to feel that try casting two lines the same weight but different density - the only difference is the drag on the lines - dunno about you but I certainly can feel the difference between a floating line and a sinker, even an intermediate sinker.
For that matter - try this
fit a bushy size 10 fly to the leader and cast - replace the fly with a bare hook. In calm conditions its quite possible to feel the difference - utterly impossible when windy.
Paul
TLT is an Italian school or style of casting - no reason you should have heard of it.
We need to get the next Outcast day and I can show you the difference in haul potential between open and closed stances.