An alternative effect could be that online ads are an avenue for better resourced established companies to out compete and stifle upstarts. Startups are always pressed for resources and running an effective online ad campaign can take significant resources.
You're surely right that some small businesses have benefited from the online ad market, but I suspect that on average larger companies have benefited to a greater degree.
[0]https://www.uschamber.com/small-business/small-business-data...
Ceteris paribus. Running a small business in most states involves more rules today than it did in 2000. (Common denominator: the cost of financial transactions due to post-9/11 anti-money laundering rules.)
to name a few: LISEN, Qifutan, Loncaster, YKYI, Holikme and SXhyf. And who could forget VWMYQ?
And it still doesn't justify Google.