However if your target of holding BTC is for long term, these altcoin season things are just meaningless noise.
We know that holding Bitcoin for the long term has always been the best choice. The altcoin season is actually a good time for most of the altcoin holders to make profit and leverage their profit into accumulating more Bitcoin. I don't know how others are doing it but if they're not doing it then most likely they're just taking the cash and not going back to the market. Waiting for another opportunity to buy some of these alts and will wait if they pump again. The best time to sell Bitcoin is subjective to be honest.
Yes, but the thing with accumulating altcoin is that they might be late or have been in the game for 3 years and not seeing a good profit. As compare to Bitcoin, in which many of us are already in the positive as we have hit multiple all time high already. Nevertheless, a Youtuber? I wouldn't blindly trust anyone specially a social media influencer. There is a huge risk if you go and follow that advise to sell Bitcoin and then invest it on altcoin? Maybe for risk takers but you still have to remember that you really have to place safe and only invest on Bitcoin. Don't be carried away by a "potential" x100 or even higher being promise by social influencer to invest on altcoins. If you don't know what you are doing by those kind of leverage, then you are putting your money at a huge risk.