These folks are explicitly looking for mid to late career, highly skilled people. Those they don't hire they're not arguing need to be paid the same. I'm pretty sure they don't have a pool of receptionists and custodial staff making the same as the founders. Those positions, if they exist, are likely done by temps or contractors.
When they mention that the pay may not stay uniform, they might be talking about creating junior positions and operational positions like technical support at a lower rung, even if the ladder stays to very few rungs.
I think successfully arguing that any venture-capital backed enterprise is socialist is difficult, to be honest.
Socialism is a society level compact that cannot be unwound the same way if at all.
It may work in short term, when everyone is part of product and tech team, and building product and valuation.
It will become a problem when junior people are paid same as senior level people that’s delivering more impact. And, when the company grows and have to hire support staff. Will they pay same salary to the receptionist?
Like literally anyone can start a team of few people that are all paid the same. It's not really that hard, nor does it require that much attention. You only need to write about it, if it successfully stays that way for a long period of time or if it scales when parameters change.