Keep in mind that it’s common to have at least one cofounder. Some times more. Start with 3 cofounders and an equal split and already nobody can have more than 33% of the company.
The term “Series A” has also become kind of diluted away by a growing list of earlier rounds: Angel, pre-seed, seed, etc. It’s getting kind of funny to see how much fundraising a company can do before “Series A” these days.
Equity is a tough topic to think about because everyone expects to have a lot, but numerically a startup with multiple cofounders and multiple investment rounds and an employee option pool and equity for early hires will end up with a lot of entries on the cap table. It becomes difficult for any one person to have >20% equity very quickly in most cases.
At startups I often had to explain this to early but post-investment hires who expected 10% or more equity for themselves on top of market rate salaries. Unfortunately the equity gets spread across a lot of different parties.