Listen, the figures that we're discussing here need to be backed up whether said by a regular person or an expert. Because experts themselves can't come up with such figures, they have to get them from somewhere else. That "somewhere" is what needs to be quoted.
Figures like these should be easily sourced if sources for them exist. This is not like an expert opinion on some countries' economy's features, where no body else might share the same opinion, but regardless, an expert's words still count.
This is talking about facts and figures. Experts can only be used for opinions. If you're using an expert for a figure, then you're barking up the wrong tree, because an expert saying that this is the figure of that doesn't make it so. Experts themselves get figures from somewhere, such as UN, IMF, etc. If this guy has nothing to back himself up then he can't be taken seriously, whether an expert or not.