I think those who are waiting for ETF approval have already bought Bitcoin and are simply waiting for the moment when after the announcement there will be a pump, perhaps to sell.
You have a point on this. It will be absurd to wait for an approval before purchasing your Bitcoin, because then you won't be able to maximize enough profits, what with you buying when price was high and all that. For me, Bitcoin is a volatile coin, and although there are factors that can cause it's price to shoot up, it's not really safe to depend on ETF approval alone because that way it would seem as if without an approval, we won't see an upward surge.