We have some of the most intelligent people in the world working on extracting as much wealth as possible from high volume trading. For someone to gain money in the market someone most lose. Imagine if we had these minds working on solving real world problems that would actually benefit society. Just like gambling, trading is zero sum.
Well, it all depends on what you referred to as lost because some may Bitcoin or other coins at let say $50 and when its value appreciate to like $60 and later drop down to $55 before they sell to them is like they sell at lost which is not so.
If the market value of the Bitcoin appreciate and maybe it appreciate because there are new investors and those that bought when its value was very little sell and make profit and at the time those new investors are yet to sell theirs then one has made any lost yet. In this case, your submission that "trading trading is a zero sum game" will not stand dude.