I think right now the disadvantages of altcoin is that there are way too many of them. At this point anyone can make an altcoin and use the coin to scam people. If we had less altcoins in the market then the prices would be doing a lot better than they are now. In the coming years, we will be watching  alot of scam altcoins failing but the problem is that as they fail, they take money out of the market with them.