You have a point. For the price of one of these kits, a pair of XI sports could be purchased. For the price of an Xray T4'16, five XI sports could be purchased with change left over. Yet we still see novice drivers buying brand new T4's, TC7's, and BD7's.
This car is an improvement over the Ultimate, which also comes in at a lower price point. It is also a good upgrade for drivers of the XI sport who want to continue using their inventory of parts.
Regarding second-hand cars, we cant compare apples to bananas.