There is nothing equal about taking from one and giving to the other. (...) What matters is the wealth and progression of the middle class and the freedom to move freely through the classes, based on ones' abilities and desires.
But reality is more messy than that, there are all sorts of people whose abilities and skills (ranked on how useful or desired by others) are a poor match for today's society. Having a system that only rewards those who fit in best is a recipe for disaster and dehumanizing/neglecting those that don't fit in / are less fit. Diversity is longterm strength, but more importantly we have the capability for rational compassion and care for others and the wealth to make supporting everyone a minor burden at worst. Anyone who has experience with family who cannot succeed financially, but brings them great joy otherwise could tell you how important compassion and care for others is for their entire family.
Setting up a system that takes away the fears and worries about living with a decent quality of life: food, shelter, health care, meaningful work, etc brings unimaginable, but generally indirect (until something terrible happens directly to you or your family), benefits to all. Think reduced crime, more opportunity for someone to make the thing you've always wanted, etc. In a perfect world, this would be common sense and giving and support of others would be voluntary, but (especially in societies that emphasize the rightness of owning and hording regardless of the impact on others) the enforcing of distribution of wealth is a useful but blunt tool.
In addition, in this particular example, capping pay has a direct benefit to the companies: the last sort of person we want running a large business/organization that is designed to outlast their tenure is someone motivated strongly by financial incentives. That sort of leader is a real risk to the organization as they will always make mistakes in their favour rather than sacrifice for the organization.