Like? can you show me a video of what you're talking about? Because there's literally nothing she can't do with her voice. She even taught her self to autotune her voice.
Enjoy the 16 minutes (the diminuendos @ ~1:30 are already sth Nicole cannot do with her voice)
Love this video. It always makes me appreciate Bey's vocals
It also perfectly explains what is meant by saying "Beyonce's voice is the most agile". It's quite incredible that a pop/RnB singer is able to do all that. She has really crafted her instrument and has become the best singer amongst all pop stars of our generation (technically, and therefore objectively, speaking).
I watched like I half of it and I definitely think Nicole is a very good singer. No doubt about it. She impresses me the most when she sings classical stuff, simply because it's unexpected. However generally speaking, she's nowhere near as creative with her runs and as agile as Bey.
When it comes to diminuendos and crescendos as well as flexibility with singing with "half voice" etc, Nicole seems to produce predictable runs way more often than Bey.