He used plethora correctly.
Meaning of plethora in English
plethora
noun [ S ]
formal
uk
/ˈpleθ.ər.ə/ us
/ˈpleθ.ɚ.ə/
C2
a very large amount of something, especially a larger amount than you need, want, or can deal with:
There's a plethora of books about the royal family.
The plethora of regulations is both contradictory and confusing.
https://dictionary.cambridge.org/dictionary/english/plethora