Companies that build themselves on selling open source software put themselves in the position where anyone else can copy them and compete with them on price, and price alone. This is clearly the disadvantage of open source. It brings plenty of advantages, which is why people do it - but you can't have only the advantages and no disadvantages of open source.
Open sourcing your product is a risky investment, and as with all risky investments, it might pay out, or it might not.
As I said before, I believe that using permissive licences is a bad idea. I have seen multiple projects choosing a permissive licence as a way to compete against an already established copyleft project, just because it's easier to get adopted by companies. I find it unfair but also a bit stupid: by using a permissive licence, they allow anyone to compete with them with a proprietary fork.
Still, there is an antitrust question (that is slightly orthogonal): if TooBigTech can offer a similar product at a loss (e.g. for free) until they capture the market, then that's a problem. And they can only do it because they are too big, and that is an antitrust issue IMO.
Open sourcing your product is a risky investment, and as with all risky investments, it might pay out, or it might not.