If the market consists of few actors, you get collusion to depress wages and opportunity (in tech you had https://pando.com/2014/03/22/revealed-apple-and-googles-wage...) but it exists across a number of industries. Your assertion assumes only good actors, which is not commensurate with reality.
This sort of collusion can also be addressed in a much more targeted way than creating laws that give workers who unionize control over major hiring decisions of their employer.
Unions in the private sector became much weaker over the last 40 years, but that was not due to the labor laws that empower unions being eased. It was due to the type of industries that unions are prone to form in (e.g. labor-intensive, high volume manufacturing) contracting in the US.
The laws that empower unions make the US inhospitable to key industries.
What's going to happen to the US electric car manufacturing industry if Tesla's workers unionize?
What's going to happen to Amazon's business units if they see massive unionization?
The consequences for a US-based operation when their work force unionizes is a major disincentive for investing in production in the US, and a major impediment to existing US-centred companies from expanding.
It's a prisoners' dilemma thing. Businesses that can move production to low-wage countries are leeching off businesses that can't move. Also, it rather destroys the concept of a nation, where workers and businesses depend on each other.
It's possible to have both high wages and competitive production facilities. That happens when the skill-set of the workforce and the infrastructure and supply-chain of the nation improve enough to compensate for the higher wages.
Forcing companies to pay wages that are above the level that they would be at if left to market forces results in parties in the US less effectively utilizing labor and capital to raise productivity. Less productivity growth ultimately means less wage growth.
The wage boost that comes from a law mandating companies pay higher wages is a one time event, that results from an increase in labor's share of total income, and comes at the expense of lower recurring boosts to wages, because the disruption to the economy caused by such a law reduces the rate of economic growth.
So laws that force companies to pay higher wages mean, in the long run, people being poorer than they would otherwise be.
Ultimately that results in the wages offered being determined by the underlying market forces of supply and demand that are far larger and more powerful than the efforts of any single party. And it is in society's best interest for wages to be determined by supply and demand and not some social agenda.
The only policy which provide zero sum benefits to corporations at the expense of workers is immigration. And that can be addressed by workers through political coordination. The primary purpose of unions is to give select groups of workers the ability to engage in rent-seeking at the expense of the wider economy. We can get political coordination between workers without resorting to unions and all the harm that comes along with them.