Whilst for many people Big Tech does literally mean size of a company - I think that generally it can also mean, tech that is harming society or our environment (which really are the same thing).
We prefer this definition, and the connection between harmful, oppressive tech, as opposed to the focus on size/revenue of the company because otherwise you risk missing the threat.
One realisation I had is that, because of the difficulty we were having in pinning down our own internal definition of Big Tech, this was probably a clue that we were asking the wrong questions.
So I propose that actually, Big Tech is a label or term that has come to be applied to publically known tech firms that are, in some shape or form, evil, or not good for wider society.
They might profit from addiction, exploit users, push consumption, create unhappy consumers, and create this larger divide within levels of inequality due to the profits they extract (often avoiding corporation tax) that are funnelled up towards their owners and shareholders. They might even be used to help political parties win power, or to advocate for their harmful policies.
So clearly if we instead think of the term of Big Tech as instead generally meaning bad tech - there needs to be a movement that raises awareness of why it is bad, how it is bad, but which critically also proposes how to stop the rise of Big Tech - or how to counter it.
This lead to a different kind of problem I was hitting.
Unless you are actively anti-capitalist in your critique of Big Tech - as in - within a capitalist society technology will always be abused by those with bad intentions - you end up advocating for what you might describe as less bad tech.
There is nothing wrong with fighting for tech which is not evil by nature - and I do believe there are ways in which we can look to control the rise of Big Tech - but again, within a capitalist system, these are all very much temporary plasters being applied to a very severe, life-threatening injury.
We want to denounce Big Tech but are conscious that the ultimate question here to be asking is really, within a Capitalist society, what does good tech look like?