I only followed your logic to its natural conclusion. You stated, “In my opinion, the reason it didn’t do as well is because... it sounds childish.” Without any further conditions, the logic underpinning your argument was: (1) Songs that sound childish don’t do well (relative to songs that don’t sound childish); (2) IUSA sounds childish; (3) Therefore, IUSA didn’t do well (relative to the prior performances of “Womanizer” and “Circus”).

So no, you didn’t explicitly state that songs that sound childish aren’t successful. However, the premise “songs that are childish don’t do well (relative to songs that don’t sound childish)” is central to your argument. In order for your argument to be logically valid, we must accept that the premise “songs that sound childish don’t do well (relative to songs that don’t sound childish)” is true.

So by way of inductive inference, you actually are saying that, to some extent, songs that sound childish aren’t successful; its imbedded in your argument.