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.
A lot of good projects suffer because of the manipulation of the price of Bitcoin, particularly if they raised funds from the public and have devs to pay. It just goes to show that even the best technology does not always win because you need a real world usecase and marketing to be successful. Some projects that can survive just about anything are RVN and 0xMR because they are mineable and raised no funds from the public. As long as people are mining them, and there is a community behind them, they will survive regardless of what happens with Bitcoin.