They should change the formula.
I notices that even 0.1 btc pump trade on the single exchnage can bring certain coins up which is totlly not fair. I bet some guys manipulate that chart to advertize their coin to noobs (who just see crazy growth numbers and start buying bad pumped coins).
Yeah noticed this on Coinedup.
For example a coin selling at 1 and buying at 2, if you buy, the price will be 2 on Coinmarketcap, if you sell the price will be 1. It's easy to cheat the price by buying very small amount to get the higher price registered.
You can also make fake order (you buy or sell to yourself), that's increasing the traded volume. On coinedup, no trade fee, so it's free to cheat the system =)
edit: bolded something very important in your post.