stop confusing affinity with nature.Kakashi went on to say jonin have minimum two affinities, I don't see what's the argument. A shinobi can use multiple chakra natures if they have the skill and just because they don't doesn't meant they lack the affinity.
If Hashirama only had one affinity he wouldn't be able to use KKG or genjutsu, if Sasuke had only one affinity he wouldn't be able to use Katon, Raiton and genjutsu all at the highest level.
Hirizen was praised because he had the skill to master all his affinities, most ninja can't be master of spades and Kakashi's statement was from the perspective of most ninja.
Nagato is another example of someone with multiple affinities.
You can have one affinity:
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but multiple natures:
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