In my opinion that Both short term and long term have their own advantages and disadvantages. With long term, you may get bigger reward without taking much hassle. On the other hand, with short term, you have to follow a lot of things.
Long term investments are sometimes risky in case of cryptocurrency space, you know a lot of altcoin have disappear and it's possible that your holding will not be existed someday. On the other hand, short term investors can move anywhere since they are updated with the market.
I personally prefer long term holding but of course only the top ranked coin.
Of course, only those who have been in the market for so long known this, for those who are saying that long term holders are dumb, probably are those short term speculators and traders or those who missed the boat and wanted to buy at cheap price by creating this idea that holders should sell. I'm not sure about altcoin, but if you have seen bitcoin tremendous growth just like in the last bear and bull run, from $3k to $69k, that is a huge profit already for holding like 3 years.