The phrase buy the dip is only a good advice when you apply it properly by buying the very good altcoins whose value is only down because of the bearish market condition. Because it is not all coins that dip that would recover their value.
For example, early this year (when the market was super bullish) almost all the projects released saw good increase in their value. but that doesn't mean it is all of them that were very good projects. After the market dip (correction), most of them never recovered their value. The crypto market is filled with a lot of scrap altcoins and the market way of sheding them off is to dip (correction). So it would be in your best interest to only buy very good coins in the market dip.
You are right, after the drastic drop in the price of crypto in the market, we can see that almost 99% of altcoins are also affected by the negative sentiment that hit bitcoin, but in the last few days the price of altcoins has increased slowly along with the return of bitcoin prices, and it can be seen if the altcoins that are in the in the top 20 on the coinmarket it is slowly improving, while new altcoins or tokens continue to decline and it seems difficult for the price to rise in the market again.