I have the following sentence from my hero academia anime.

```

    つくづく あの入試は 合理性に欠くよ｡
    
```

The english subtitles for the show have this as the translation "That entrance
exam was definitely not rational enough."

I'm confused at how に is working here. I know that に can be used for nouns
that take the copula (na adjectives) to turn them into an adverb but 合理性 isn't
one of these na adjectives. I would think を or は would make more sense here.
Is に perhaps acting as a substitute for は here?

I've ruled out this acting as an indirect object marker and a direction
marker. From there, I'm pretty clueless as to what it's exact function is
here. Can anybody help me out here?
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2020-01-25T20:01:51.907
74070
2020-01-25T20:01:51.907
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question
particle-に
How is に used in the following sentence?