To recap, I think there are some very key issues to a successful JLU 3pack.
There is one 3 pack that was too good, and too bad.
Superman, Batman, and Wonder Woman.
These days, DC refers to them as their "Trinity" (and the comic of that name is a good old school read, but I digress).
To JLU toy fans, this packout was a waste. A 3 pack with nothing new in it. No reason for them to buy it. With no demand from collectors, it seemed to clog the pegs. We could see no good from this, only wasted space that could have been filled with characters that we did want.
For parents, it was too good. Both Superman and Batman in the same package. The rumor is that Walmart requested this packout. Yes it makes sense, from one point of view. But from another point of view, it makes no sense. This pack reduces the amount of purchases mom or grandpa has to make. Instead of buying 2 packages to get Superman and Batman, now they only needed to buy one. This would cut overall sales in half.
These days this 3 pack is a thing of the past. But its still interesting to note how something so good for one group of customers can be so bad for another.