Holding more altcoins is recommended because we cant predict which one altcoin rise in the future and which one dies. So by doing this you could reduce the risk.
This is true and I agragree on this,since the crypto market is dicy,one can't tell which altcoin will be valuable in future, to avoid regret more people decide to hold for a while.
I'm actually doing it with the same reason as yours. I also don't want to miss any sudden pump in price with other alternative coins. I believe that those coins has the same potential as bitcoin. I prefer those alts that are already well established since I can hold them in a secure open source multiwallet called Hodler, this way I can be assured that it will be safely stored even for longer period of time.