If they hold a long time, they are investors/holders, they aren't traders. Yes, they won't get losses if they know the cycle and they can be patient to wait for the bullrun season. Hold Bitcoin for years is quite safe because Bitcoin always reaches a new ATH in each bullrun season period. But for altcoins, we must be careful. There are altcoins that never reach their best prices again. So, for the long term holders, it is better to hold Bitcoin.
So far, BTC has proven its potential by consistently setting new ATHs in each cycle, but only a few altcoins can achieve that. This season, ETH hasn't even set a new ATH, causing the crypto community to panic and fear that an altseason won't happen.
I also believe that altcoins should only be invested in seasonally; holding altcoins from one season to the next isn't a good idea. However, at critical times, shifting attention from BTC to altcoins is a good suggestion, especially when investors see an altseason starting and altcoins generating higher profits than BTC. I just don't know if this is the right time, so I'll keep DCA a few top coins to not miss out on this season's opportunities.