In my opinion, you should take the difference between their market salary and the salary they're being offered, and consider that an investment by the employee at the upcoming (not past) valuation.
For example if they're in SF and they're hiring a senior first engineer that would maybe make 250k elsewhere, and they're offering them 125k, and they would take the classic 7% for 125k, then 7% is a good starting point. (Of course if they already have the YC investment, then that would go down dramatically)
If that equity vests over 4 years, then frankly maybe 28% is a better starting point.
But what's fair isn't really relevant. What's relevant is what the market demand and supply is. If there's some dolt who would happily take 1.5% as a first engineer ("founding engineer") for a $125k salary cut, then the founders would be idiots not to take that deal. And frankly, if that $125k salary cut gets them their dream job, then maybe they're not even dumb for doing it.
I think what you are actually describing is that you should value equity at zero. If to work at a startup you would need 28% equity you are describing a founder. That's fine but there is an enormous difference between these two things. There is also the question of where the $125k comes from to pay your base.
Value equity at zero? I am not sure what you mean by that. If an employee sacrifices $500k to work at your company, then it would make sense to compensate them with $500k worth of equity is my point. The 28% is tongue in cheek, if you're so early that the amount of equity needed to compensate your first hire adequately is 28%, your company hasn't really started yet, and maybe you should just consider them a founder.
Bingo - if you need the kind of person whose market rate would be 28% of your company. They are a founder, if your don’t need that person… fine, but the “this is the industry standard” line is bogus.
In my experience, "fair" is almost irrelevant within a capitalist business.
Good capitalist businesses buy at the cheapest price they can, and they owners focus on balancing competing resources (control, dividends, ownership, status, information, etcetera...). However: people run businesses and people are not rational economic actors.
A good question is: what amount of equity can you negotiate? What do you have that will convince owners to share their ownership with you?
If you are negotiating with VC, then I think the game board and the rules of the game are already rigged against founders and employees. VC sets the rules and the mileau to play the long game, and employees are lucky to get a few leftovers.
You can be a founder or join a self-funded startup, that will give you a better chance of "fair" treatment, especially if you have the skills to join people that have high integrity.
In theory if you can marginally add 10% to the business value you should be able to argue to get some amount of that. However measuring an individuals effect on a business is usually really difficult (even consultants or businesses that specialise in increasing value usually only capture a tiny percentage of the value they add).
Also different people bring different resources to a business, and anyone with a monopoly on a resource can negotiate for more shareholding. There are idealistic economic theories for how people should bid in multi-party negotiations. Note that even though multiple people may each increase the value of a business by more than 50%, that doesn't mean each should get 50% of the shares (and obviously can't if more than two want >50%).
Generally if you need to ask for shares then you have already lost the game. Either found a business and put yourself in charge, or have something the owners want and demand ownership.
Disclosure: made small amounts of money as part of a self-funded startup joining high integrity co-founders. I've had little experience of VC funded companies or employee shares. Our SaaS business was doing something we'd done before and it was started decades ago when things were "easier".
