Just because one person wastes money, it doesn't mean that someone else gets rich. If the employees spend their income on low-margin goods or services (food and clothing are quite competitive low-margin sectors with high labor costs), the money has flowed from investors mostly to laborers.
My thinking is that spending gets split between richer and poorer people. The former buy assets with it, but the latter spend it on living costs. Each time it circulates, typically some goes to richer people and stops circulating.
Various things could disrupt the resulting increase in inequality. The Black Death and World War 2 are both supposed to have done so.
Money doesn’t really get “split”, it flows, and the where it goes each time it is spent is what determines who makes how much. You’re right that some people are able to accumulate, but that’s not a default, and the money usually doesn’t stay put for long.
