Chloe NP gain vs Squirtoria's

It basically already does without any CEs. Her per-hit gain rate is 0.38% while Arturia's is 0.59%, but her arts cards have double the number of hits. One of Chloe's skills also charges her NP.

Even if she can't match it, Chloe is a pretty strong ST Archer welfare who you can NP5. And that's pretty considerable boon for your Saber boss hunts.

Any starting NP/NP gain CEs are good for her, if you're looking to NP sooner or more frequently during the fights.

Notice that the previous comments are missing a important point of why Archturia np gain is considered to be so high: check at her NP refund: 20% fixed at OC 1 + 10 hits with 0.59% plus her own arts buff making it even stronger and you get the picture. Just look at videos and see how she will pretty much always end her NP with 50% or more charged.
Once she gets her motor running, she don't stop.
Still, Chloe is a fantastic spammer, almost to her level, so yes, NP5 Chloe does more damage than NP 1 Archturia.