You want to charge based on the value that you deliver.
You can have small teams with large per capita usage, and large teams with low per capita usage. You ideally charge a price that each customer is happy with and that makes sense for your business. If you can't survive with 100x or 1000x as many customers at this pricing tier, you either take it off the price list immediately or when you get n additional customers of this tier (if you're still testing for product market fit).
The ideal price list repels potential customers that are a bad fit for your business. Doesn't make anyone greedy or customers bad people - just that a firm has a higher cost base or a specific business/individual won't get enough benefit from the product offered.
> You want to charge based on the value that you deliver.
Charging per key reduces the value in my opinion, exactly for the reason I stated above. It puts blocks at the point where the product is most useful (Adding a key).
I can live with extra cost when a new developer is brought on board. There's already a few things I need to buy to bring them on, and this is a reasonable extra cost. But adding charges when I add key adds friction exactly at the point where I want the product to reduce it.
I think per developer is more fair and still a good approximation of buying power and utility.