How are they going to deal with the fact half of their reviews on Google Play are 1 star, and their average is now 1.x star? Google isn't going to bend over backwards for them to delete legitimate user reviews.
Review recency matters in both app stores, AFAIK. It'll end up back wherever it would normally be as the review bomb ages out.
Android isn't the largest share of smart phone users in the US, and it's still 5 stars on the iOS app store.
Robinhood is only available in the US.
Which is why I qualified that. The numbers I've found indicate smartphone users, in the US, favor iOS (greater than 50% market share). So 1-star reviews in one of two app stores, and the app store with fewer users, won't be the thing that undoes Robinhood.