Some altcoins can be held for the long term but the majority of altcoins should only be treated as short term though. I don't know since people have seen many altcoins being so high compare to themselves a few years ago and must think we have to hold altcoins as a long-term investment but not many altcoins able to hit that big.
The ones who are able to increase and are at a high value are the Altcoins that are already popular and strong in the market because they already have a large community and enthusiasts so that they can be very suitable for the long term, while for new Altcoins it still takes time and a long journey to reach this is proof of that in the crypto space.