I think this is a slight perversion of the truth. A union that relies entirely on industrial action (a.k.a. strikes) to get a company to change, isn't a good union. If a union walks into every negotiation with just an ultimatum, then very quickly the otherside is going to get fed up of their bullshit.
Ideally a union should be working closely with senior leaders to find win-win situations for both employer and employee. An an obvious example would be preventing Andy Rubin from getting a $90mil payday for sexually harassing people. Clearly that's not only a serious injustice, but was ultimately always going to end up public and damaging Google brand.
A union could help senior leaders find a better solution, part of that would be providing representation to those sexually harassed so they could bring a stronger case, and make it much easier for other senior leaders to throw Andy Rubin to the wolves.
If the solution is already of economic advantage for Google itself, you simply don't need a union since it is already in the economic self-interest of Google to apply the solution. Employees unionize to have leverage against the employee for topics that employees have an interest in, but are of economic disadvantage for the employer (historically in particular salaries)
Doing crime, cheating, being abusive, generally are more profitable than not doing it, in the absence of consequence. 'The economic self-interest' of Google is to be absolutely monstrous, if and only if it can get away with it.
And since it can…
If those unionized googlers are worth their salt, can't they use more aggressive negotiation tactics, at least like a DDOS?
You must have not met the publicly employed unions we have in other countries. Teachers, nurses unions in my country for ex. threaten (and sometimes they do) all the time to down their tools to relative success. Sometimes the only way to get a point across your deaf employer is the way of the iron fist.
It's also illegal.
Then you find another pretense for firing many of them.
Addendum: There exist so many oblique "performance metrics" you can apply on the employee to find such a pretense.
It is not clear whether these employees are actually in a good position for negotiating. The idea behind unions is that an employer is not willing to lay off all the employees that are unionized (because this would lead to a sharp decline in productivity and thus KPIs). I consider how many products were scrapped by Google as quite some evidence that Google would be nearly as successful if it fired the unionized employees and continued working with some "core team".
This does, of course, not mean that I endorse this reality, but when you negotiate, you better know what leverage you actually have.