As for Rihanna and Katy the answer is easy. Remixes, 69c discounts on itunes and radio payola. Or how else would anyone explain their low networth compared to Gagas netwoth after ofly 4 years. Bruno on the other hand has talent and is releasing the right singles at the right time.
So now crafting catchy melodies is a bad thing, oh please look at some of the biggest timeless hits, they all have that chorus or one line which everyone sings when they hear the song, as for bruno, people are still trying to find excuses for him smashing like that, I said it before bruno mars is a producer at first, he understands the beats and he has a huge musical background which shows in his blending genres' hits, not to forget he's an amazing singer & live performer, he's the whole package, he can literally go from jumping on stage and dancing with his band to standing solo on stage singing a ballad without any music playing, he's like the Billy Joel of this generation.
People act as if the discount made Katy to have three 5x platinum in the TD era, the discount thing only helped her to get an easier #1 with LFN (even though it lasted two weeks in the top ) and she's a radio darling, the same applies to Bruno.