First, “no complexity bounds on the trader” doesn’t mean we allow uncomputable traders, we just don’t limit their time or other resources (exactly like in Solomonoff induction). Second, even having a trader that knows everything doesn’t mean all the prices collapse in a single step. It does mean that the prices will converge to knowing everything with time. GI guarantees no budget-limited trader will make an infinite profit, it doesn’t guarantee no trader will make a profit at all (indeed guaranteeing the later is impossible).
First, “no complexity bounds on the trader” doesn’t mean we allow uncomputable traders, we just don’t limit their time or other resources (exactly like in Solomonoff induction). Second, even having a trader that knows everything doesn’t mean all the prices collapse in a single step. It does mean that the prices will converge to knowing everything with time. GI guarantees no budget-limited trader will make an infinite profit, it doesn’t guarantee no trader will make a profit at all (indeed guaranteeing the later is impossible).