You may also have been thinking of "favoured class", which was a thing in 3/3.5e, and humans had "any" as their favoured class, which significantly reduced multiclassing penalties, and between that and the extra feat at level 1, it made Human the obvious choice when going for certain complex builds. But that was also done away with in 5e, we have no multiclassing penalties, but that's yet another Human trait that emphasised adaptability and flexibility which they don't have anymore.