Without being able to sell shares, a wine company that makes a profit can only grow by reinvesting their profit. E.g. it cost 100 tokens to set up the shop, it grows by 15 tokens a year, it has to wait 7 years before it can set up a different shop. With the ability to sell shares, once they prove a profitable business model, they can sell shares in order to grow the business into other areas.
Without arbitrage, a wine shop that returns 15 tokens for every 100 invested might be able to sell shares at the same value as a meat shop that only makes 8 tokens for every 100 invested. Even though the wine shop is more popular, more profitable and providing more value to the market, it is forced to grow at the same rate as the meat shop.
We need a system of allocating resources efficiently, and the economy will provide the most value possible. This is what arbitrage does. And you'd want pretty smart people doing it, as these decisions can cause the success or failure of companies.
To put it in other terms, the footsoldiers might do the actual fighting, but I prefer to be part of an army with generals that decide where to place troops rather than one composed entirely out of 'actual fighting people' (or as you call it 'real things produced with real skill and effort, goods such as meat, wine, cars').
There are ways of cheating the system, and I support strong financial regulations. But that doesn't mean these jobs shouldn't exist in the first place or they don't provide any value.