Except a level 9 rogue hopefully won't be anywhere near a CR 9 Cloud Giant (one of the best Passive Perceptions in the game, btw, so nice choice...), especially more than one!
But anyway, the average "monster" WIS is about 12 (slightly higher), so a +1 bonus. Many foes aren't proficient in Perception (the cloud giant is), so your typical passive perception is only 11. Even when the DM rolls a contested roll, the odds of that +1 beating that +12 is pretty darn small (about 11%). In other words, the rogue sneaks successfully on average about 90% of the time. THAT is a bit too high in our book.
Well, adding advantage was more just to appeal to those who think a flat +2 "isn't enough" for the poor rogue.
We already allowed a background skill to be chosen instead at the cost of the other background skill. This way, even Rogues can do it by default to gain a third expertise.
No one at our table thinks the rogue is a tad weak in any way. In fact, most of us feel the rogue's feature of expertise is too much and throws the idea of bounded accuracy out the window. As I wrote before it leads to some pretty ridiculous ideas really. Even with a flat +2 bonus, expertise makes rogues better at what they want to be better at in many cases and for no ASI investment, freeing them to select feats or use the ASI in other places if they want.