If you have regulations by revenue/employee count then the companies will restructure themselves to be below those thresholds.
E.g. could Facebook run with 20 staff? Would Facebook and its shareholders be satisfied with 20m in annual revenue.
This scenario requires trade offs. My opinion is that monopoly, political and market dominance is a sub-optimal outcome
It could similarly avoid large profits but avoiding large revenues works be trickier. But I'm not an expert in these things, so maybe it's possible if you really know what you're doing.
There are multiple private multi billion dollar companies and I wouldn't be surprised, if they all have less than 100 shareholders.
All of the major tech companies are publicly traded.
Being publicly traded is also a major risk factor for hostile corporate behavior, because the top executives of private companies tend to be the owners and care more about the long-term than short-term profits, so it even makes sense as an explicit policy choice to regulate publicly traded companies more than private ones.