Ummmm....Bellagio is one stop on the tram. Crystals (City Center) is one stop. And, Aria/Monte Carlo is one stop. After getting off the tram at the Aria/Monte Carlo stop, a left turn takes you down an escalator that leads into Aria. A right turn takes you to the entryway to Monte Carlo. There is no tram that runs between Aria and Monte Carlo. Those 2 properties are at the same tram stop.
You can certainly walk from Bellagio to either Aria or Monte Carlo utilizing Vdara. It's not a bad walk at all.
Again, one tram is now an "express" that travels between Bellagio and Aria/Monte Carlo, without stopping at Crystals. The other tram is unchanged; it stops at Bellagio and Crystals and Aria/Monte Carlo, as before.