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.
I definitely agree with what you are saying. During the times of a huge bullrun almost every projects makes some nice gains even those that were already dead with no volume for a few years. I still don't know why this happens or why someone would by coins like that but it keeps happening during bullruns. Once the bear market comes it becomes obvious which projects have a strong foundation and are here to stay even if the coin loses 90% or more of its value. So in that regard a bear market is much more helpful to determine which projects are actually solid and which projects where just created to benefit from a bull market.