I'm Canadian, but our small businesses are definitely very reliant on targeted advertising. Anecdotally, I know a few people with their own businesses that will only use Google or Facebook targeted advertising, because it's cheap and they get a better return on ad spend since they can target a local subpopulation.

Bigger outfits have the means to litterally crush the small ones in this arena too.

It doesn't actually work that way, at least not entirely. Platforms don't necessarily show the ad with the highest bid, they also take into account relevance to the user, so Walmart can't just swoop in and take all the ad spots. Even if they could, platforms don't charge unless the ad was shown (or clicked in some cases), so worst case scenario small businesses just wouldn't have their account's ad dollars spent. This definitely isn't the case though, because 70% of small businesses advertiser on social media.

There are additional studies that show this as well. I'll try to find some that aren't funded by Facebook or Google, so far this one is pretty interesting:

https://arxiv.org/abs/2307.09035