When Luna collapsed the previous position was ranked 8th, ranking and marketcap never guaranteed safe, always alert is the best thing so we don't regret it, if there is a coin that we hold and drop more than 5% a day then always observe and immediately take decisions or sell before losing bigger.
Agree CMC is only a reference to see the trading performance of a coin not to determine whether they are good and safe as an option, even almost all altcoins are not safe to choose because all are at risk, developers may dumb away the coins they hold or leave the project without you being clear about the continuation of its development
But a 5% drop in a day is still quite reasonable in my opinion which is dangerous if the decline reaches tens of percent in a day it's a bad sign and maybe the holder is a little too late to sell it.
Regarding Op's question, it's quite strange because even altcoins are hard to predict in the short term let alone the long term, and the question was made in 2021 where if he realized it would be a good time to sell the altcoins he held
If the coin is at the top ranks then their performance is also great. It's okay to ride on them but we should be aware that their rankings are not fixed so we should watch out for what can happen on our coin. We need to sell and replace them if necessary and we need to check cmc again if what coins are performing better.
5% drop might still be fine but we shouldn't wait before it is already too late but if we think the drop is already grow huge then I think much better if we will just hodl and pray and maybe there are miracles that can happen than completely selling it at a loss. Op's goal is for 2025 not 2021, that is why he didn't sold his coin's.