HYIP could have some benefits only if you are on of the first investors. But after earn % you should take right moment to leave hyip. But as many already answered, at the end all benefits goes to the hyip owner.
Yes, who invests first has more chance to make profit with it. But if the scheme only bring few investors everybody is scammed, because there is nothing to be paid. The HYIP owners are always looking for referrals, and referrals of referrals, this way they survive for a bit more time, pay the first investors, share the "it's paying" message and scam all the rest on the end.
It is the marketing strategy they usually follow, that is what you called a pyramid scam, you can never profit from that kind of investment in a clean way, although you profit sometimes but knowing you get that profit while others got scammed it would not be fulfilling to you and that is not success anymore.
HYIP surely is a pyramid scheming scam. Only people on the top will benefit from it with the effort of people on his downlines.
So, downline will work very hard for there money but they don't know only people from the top will benefit from it.