Think of a new player's point of view. This player cannot do dragon 20, hell, he probably is still struggling to get past level 10 of any dungeon.
So he gets the pass, wins a full 6-star set, with ores to go along. Chances are, half the pieces will get very bad rolls. So he can use the ores, and try to improve at least one of those pieces, and voila, the 4-piece set can now be used.
Is that 4-piece set OP? by a veteran's player's standards, probably not even close, as suggested by the extensive math done above. But for a noob? It sure beats the 3-star life or offense set you're given early, or even the 4-star ones that come not long after.
So, i guess this FP has some value to some people, probably that the values rises for new guys, and falls for old-timers.
Perhaps they felt they could reach enough people with this, and i doubt this forum will be a good indicator of the real answer. With the staggering number of players overall (and maybe 100 of those come here to chat LOL), there's a LOT we dont really know about the player base, isnt there?