This is true in every negotiation in every part of your life. What does equality even mean in such a context?
Epistemologically, there is no way for you to have enough context about either the other party or the other party's other counter-parties to inform your negotiation in a meaningful way. The only facts available to help you price your services are what others will pay for it, but this is not the same as pay transparency. Pay transparency is the price of other people's services, not yours, and it doesn't take into account your context.
Ethically, only you can know the value of the transaction - which is not the same as the amount of money exchanging hands. By that standard, employers are nuts to ever employ anyone, since employees don't pay their employers (except in North Korea and some unions). Only the employer can know the value they get out of you, in the totality of benefit your provide - though even then their information is very limited. And only you can know the value you get from your employer - again in the total benefit they provide both in cash and non-pecuniary factors.
To put it another way, you wouldn't ask for the same income from, say, Pornhub, Phillip-Morris, Google, and Watsi. So why do you think those companies should treat their employees like an undifferentiated mass of goop?
