Unions make the employer-employee relationship in the workplace adversarial instead of being tightly focused on making the best products possible for the consumer. They are both harmful and unnecessary to the American video game industry overall.
In an imaginary world of kumbaya corporate culture where people respect one another and aren't being incentivized, top-down, to drive profitability for parent companies and shareholders, you might have a point. Unions exist and came into existence because this really isn't the case. Employment is a contractual negotiation: labour and skills in exchange for pay. Individuals are easily replaced (especially in low-skill areas), but entire workforces are not. Unionisation makes that negotiation fair. It has, however, seen a massive decline during the last twenty years - did it lead, as you suggest, to employers and employees being suddenly unbound from adversarial relationships to 'make the best products possible for the consumer'? No, it really didn't.
What actually happened was a colossal shift, across almost every industry, toward gloablisation and outsourcing. Manufacturing was moved almost entirely to cheaper, less strictly regulated developing nations and responsibility for the staff moved to third-party outsourcing companies. Closer to home, workforces shrank rapidly, with salaried, full-time positions giving way to agency work - individuals who would labour away for a company that no longer recognised them as employees, because their contract was actually with an agency shell company. In this way, companies could offload their responsibilities as employers to another company, whilst retaining full access to the labour force they needed: a simple sleight of hand that sidestepped all the rights won by unions over the previous century.
You might think this is the way things should be - you might think this is just good business and there are no doubt arguments to be made in both directions, but the idea that employees and employers would just get down to work if the unions got out of the way is a myth sold by a media class who've benefitted from this new system rather than lost out. The groundswell of dissatisfaction and anti-establishment sentiment you've seen over the last decade suggests there are a lot of people who aren't benefitting.