Ya I guess for long term only Bitcoin and ETH are worth holding. All others are maybe good for few years max, but then usually drop in value. Just see EOS. Biggest ICO till date and even after 2 years still around 10x less value from the original ICO value. And some projects that try really hard may also fail due to complex regulations by govt. or simply no demand for their product in market.
For Bitcoin and ETH, you will have a lot of profit if you hold them in the long term. Because those are the biggest cryptocurrencies in this market. And for altcoins, you need to be really careful because the price could collapse and die in the future. Also never invest long-term in new projects because I'm pretty sure they will go down many times compared to the prices of ICOs or IEOs.