Never hold any altcoin for long time. It is possible that the coin will be lost forever from all the market, there will be no volume at all etc etc. Because you don’t know what's going to happen within these long time. There are a lot of examples, many coins were in huge boom in 2018 altseason but they don't exist now. Even if they exist, they have no volume.
Yes, indeed, investing in altcoins for the long term is not suitable, because the risk is very high. and I've experienced long term investment in altcoins, but in the end I suffered a very big loss. and now I give up investing in altcoins, because the risk is very high.
It depends on the potential of an altcoin. There are still lots of altcoins that are worth investing in the long run specifically those on the top 10 market cap but most of the altcoins especially the new projects are just good for short-term investment. You only have to check on their potential and always invest in well-established coins. Coins like ETH, BNB, and LTC are actually good choices because we have seen how they could reach a good value during the bearish season.