Holding for short term isn't a good idea unless you are a trader or you are buying Bitcoin for the long term.
Now if you are saying that holding Bitcoin isn't a good idea then you might be wrong. It will depend on the plans and target of the investor.

Bitcoin isn't even reached the breakout of $21,000 like you said but the media is hyping it already and they are interviewing different crypto investors.
Moving to alts isn't a bad idea though but if you are a trader, possible you move to alts as they are more volatile and you get more profit to it than Bitcoin but on the other hand if you are an hodler then just buy Bitcoin but wait for a correction to maximize your profits.

Overall, moving to alts isn't a good idea unless you are a trader and preventing those investors into holding Bitcoin isn't a good idea too.