Since this did not receive a reply, in Ask a ski Pro, let me give it a shot since it crosses into gear head territory. I think it is more of a gear forum topic as well.
You will often hear the term "forgiveness". A ski may have a more forgiving flex and sidecut; or it may be deemed an expert's only ski. Much of that has to do with the longitudinal flex (lengthwise) of the ski. A ski with a softer tail tends to move through bumps without transferring as much of the slope variation to the skier, which in turn can throw the skier for and aft (generally into the backseat). A forgiving ski, may also tend to have slightly upturned tail or a pin-tal design that allows the ski be be more easily released and skidded.
So why would someone want and "expert" ski? A stiffer ski takes more force to decamber into a turn. That means it will support heavier weights and higher speeds while not over-flexing. A strong tail will hold onto a carved turn harder and to be skied well, requires a release that tends to be a more expert skill. These skis tend to leave a less experienced skier sitting on the slope if they do not stay forward and balanced. I'll leave it to the pros to answer that more specifically.
These are generalized characteristics and there are many variations of skis being produced today that may be a soft-expert carver or powder ski. In general though, longer, stiffer and wider seem more associated with experts, and shorter, softer moderately shaped skis seem to be preferred by learners. Your G30s were stiff, with a giant slalom sidecut and racing heritage. The 109-69-96 shape was considered mid-fat when it was produced 8-years ago. It is now on the narrow side. This ski evolved into the Supersport series and eventually to today's TigerSharks.