In terms of registrations, sure, but what about surface area? I can only think of very small pockets of places where the heavy majority of establishments are part of some megacorp

The suburbs are especially bad....

In a lot of small business it are the land lords who get the best deal by a huge margin.

but where do most people actually work?

Still small businesses.

JP Morgan Chase don't agree with you in 2014:

"48 percent of all US employees work for small businesses, down from 52 percent in the early 2000s."

https://www.jpmorganchase.com/institute/research/small-busin...

The NYSSCPA didn't agree with you in 2017 either:

"Since 2014, the latest year for which there is census data, this is no longer the case. At this point, 39.2 percent were employed at either a large or very large company, while 26.5 percent worked at mid-sized companies and 34.3 percent worked at small companies."

https://www.nysscpa.org/news/publications/the-trusted-profes...

Atkinson & Lind ("Big is Beautiful") didn't agree with you in 2019 either, specifically taking on what they call the "myth of small business as the engine of job creation"

https://thereader.mitpress.mit.edu/small-business-job-creati...

The Small Business Administration didn't agree with you in 2020:

"According to small business statistics from SBA, small businesses make 99.9% of US businesses and employ 47.1% of US employees."

https://smallbiztrends.com/small-business-statistics