If Bitcoin price pumps from $1300 to $3000 in few hours, nobody would make profit from it, because the exchanges wouldn't allow you to sell your Bitcoins and make the fast profit, it would bring a big loss for exchange sites.
Do you agree with this?
You can make quick transactions on many exchanges like poloniex. Exchanges like Coinbase however are not set up for quick transactions.
Exactly, that's why I disagree with the OP because you can actually benefit for a few hours and not necessarily that everyone cannot benefit, some can actually profit quickly from the exchanges.