This solution to this "core paradox" is the idea of gains from trade - https://en.wikipedia.org/wiki/Gains_from_trade
If everyone has the same capabilities and preferences, then the economy is a zero-sum game like you've described. In some fields, that's close to true, and those fields tend to be low-margin commodities.
It's one of the core paradoxes of economics. I want a cushy job with great pay, but when I go shopping I implicitly want everyone else to have a shitty job with low pay. There's a name for this paradox but I'm forgetting it right now.
It's very similar to the paradox of thrift: it's in my interest to save, but for me to save someone else must be spending. If everyone saves nobody can save.
Almost everything in economics is a paradox since there are two columns in accounting-- every transaction has a counter-party. It's bizarre for something not to be a paradox in economics.