But, yeah, somebody with a stronger economics background (than my undergrad degree, which I've never used professionally) would have to do some calculations on whether preventing mass corporate ownership via taxation would be a net positive for the market as a whole.
I tend to suspect it would be positive.
For example, a company in nowhere-ville develops Mr. Fusion (home edition) and needs to expand rapidly. Rents and land prices double overnight which results in the cost of labor rising which slows expansion.
There are many opportunities for rent extraction in capitalistic systems and some degree of rent and speculation are necessary to establish a market but when society allows for excessive rent taking and speculation it becomes dead weight on productive investment.
For example the “billion dollar industry” for sand that makes computer chips (https://www.wired.com/story/book-excerpt-science-of-ultra-pu...) is an example of companies with little or no investment in the technology around chips who were able to extract large sums of money simply by controlling a sand pile.
It's easy when you have a nebulous and noble goal, but you have to define it in terms that make sense and can be quantified and defined. Otherwise you'll just create a "Ministry for Company Fairness Contributions" filled with angry people that will abuse their powers for any number of reasons falling on the "evil/noble" scale.