Nilou only has two archetypes, both which depend on 5 stars (one of which isn't even released yet) to make an actual good team. It's a problem because you're extremely limiting in your options. If you don't have Kokomi, you have no good defensive option. And you need a healer or a shielder because Bloom deals self damage. your other choice is Barbara but Barbara isn't going to be nearly as effective. You will also need Nahida because currently both our dendro characters do not synergize well with just Bloom. Bloom alone is just extremely weak because you cannot use Electro to cheat and double your bloom creation, so you're stuck with a lot less blooms than a Hyperbloom or a Burgeon team that just uses Fischl. Right now we can only make Nilou - Kokomi/Barbara - DMC - Collei, else you don't have a good team. You can't switch anyone for anyone else because there is nobody else you can switch. DMC and Collei are basically there just to apply Dendro, they can't do anything else. And there's no telling that future characters are going to work with her either. Who knows when a dendro or hydro shielder will be released? When will we have 2 good dendro units for her to work fine.
She is too restrictive in the sense that you can't do much with her. You can just ignore her passive and just play her in Taser or Vape, but that's just not very fun to do unless you really like Nilou. You're basically wasting your Nilou since she is not doing anything
For off-field, Nilou should activate the third dance step then only it will create that ring, before that you can either have aoe or single dmg. I think about restriction for burgeon and hyperbloom, they compensate with bountiful cores for that reason, although I am not sure how strong bountiful core dmg would be as compared to hyperbloom. But the reason we all are talking about hyperbloom is that everyone has 5 star electro unit so people feel it is restrictive and I get it. But one cant says she is restrictive in general or a bad unit. And we cant compare Nilou with sheer raw power characterm, her strength lies in elemental reactions. Her ease of applying hydro for both single and aoe (on field as weel off field) which makes her flexible in the application. Thatswhy hoyoverse introduced as a support character which can change/amplify elemental reactions. Usually we see buff based character and praise them a lot. This is just a different kind of buff in my opinion.
I do agree one needs Kokomi, but from a non-meta and F2P perspective collei, dendro mc, barbara (which all are free) team would provide sufficient dmg with the low investment. I think comparing Nilou with Yelan and Ayato which is not fair as those playstyle is different and Nilou playstyle is new and which is yet to be discovered properly.
Nilou's attacks don't have much AOE though. You won't get AOE until your ring, and as far as I know it doesn't deal damage.
The bountiful core damage is buffed by your HP. While it'll make up in damage, it won't make it up in utility (like using Electro to double your seeds).