This was kind of true early on, and got less true both as the size of the nobility grew (especially in countries like France and Russia, which had serious nobility surpluses) and as a professional class of government emerged (by the time you get to Samuel Pepys, you're talking about largely a professional government). Even before that in practice many or most government functions were carried out by appointed or elected commoners.
To take a ridiculously over the top example, take the samurai class in the Tokugawa Shogunate. They were about 10% of the population, and by and large weren't really allowed do anything much at all (beyond wars, but there were no significant wars during that period). 99% of them were pure drain on the economy.
> as well as the investor class
This is way more dubious. Obviously it depends on the time and place, but in most times and most places it was anything from socially unacceptable (England) to effectively illegal (Roman Republic/Empire) for aristocratic landowners to invest in non-land things. What little investment in productive projects there was was largely by merchants, money lenders, and later banks, all generally commoners.