It's more than 10% that it has cost us. There are a lot of ripple effects and multipliers, not only related to pay, but also to working conditions, autonomy, and quality of work.
That said, in the long term, the companies that engage in these collusions lose because non-participants have a larger talent pool. Cartels like that are only stable if they can muscle out or absorb non-participants, and it seems unlikely for technology employment.
More onerous is the collusion among VCs, both on the discussion of terms, and in their tendency to think as a group about who they like and who they don't.
It seems to me that most VCs want to become part of the club that already exists, not compete with it. This is probably coming out of the assumption that the most well-known VCs get the best deals. I don't know how accurate that is.