I realise that this is an oft recurring topic and hesitate to add my thoughts ..but
Yes the balance point will move significantly as line is let off the spool, however, when fishing most of the line is on the water once cast so its only a few foot outside the tip and the length of the line in the rings that act as a lever one way. The other lever is easier which is the mass of the reel+residual line which is only ever a few inches from where you hold the rod so the lever action is small. The change in mass of line+reel is not very significant as its only acts over a short distance My conclusion is the balance point may move a bit while fishing, but its probably negligible.
When casting its a very dynamic process, with no slack in the line, so most of the forces are due to accelerating the line outside the tip acting on the long length of the rod. You want to be able to feel this as its the loading of the rod if you oppose it with your wrist/arm.
With a heavier reel the static balance is closer to your hand, lighter the balance is further up the rod. If this was just a rigid stick with a weight near the bottom you could only push it forward and back without it rotating if you held it exactly at the balance point or applied a counter action by clamping it in your hand and adjusted your wrist.
I think its these two points that compete while you cast - you need to feel the dynamics and this may be masked by the static swinging of the rod if its a long way out of balance.
Given the general light weight of modern tackle the differences probably boil down to personal preference. If it doesn't slide out of the palm of you hand when you pick it up its probably not going to be a problem

RogB