The RMB is a fictitious currency because a) the central bank is politically controlled b) there are currency controls c) lending is driven by the state and d) it's opaque.

The Chinese government has magical monetary policy powers, they can do anything.

The US has a fair bit of transparency, no political control and no capital controls. That adds up to a fairly 'fair market value' for USD. They can get away with shenanigans, but not remotely like China.

The Euro is the strongest of the big currencies, mostly by virtue of the fact many countries share a currency, and they are all afraid the other would print money and play games ... so in effect you get super strict rules.

Euros are backed by assets according to rules. There's some sneakyness, but it's all papered over with rules.

The USD is backed by the US gov, and since 2007 a lot of real estate. Also, because it's a seigneurage currency, it's kind of backed by the fact everyone around the world uses it.

The RMB is just whatever the party wants it to be worth.

China wants everyone to respect the RMB, they want to make more international transactions etc. but for that the rest of the world needs to see it's reliable. But in order for that, China has to play by a set of rules and not play harry potter with money. But they want to keep the magic wand (it's rational for them to want that power), so they will have a hard time making RMB go much further than their immediate periphery. Nobody wants to hold RMB.