Its not good to mixed it up knowing that there are lots of attacks happening which those people need to avoid. If it happen that they made a mistake on any of those coins they transact, they might get wiped out and lost all of their holdings.
So your suggestion is really good because separating on different wallets is best option to do here. Because they can avoid those potential heavy damages brought up by these type of attacks
Bitcoin is more valuable than altcoins and in long term, Bitcoin is a safest cryptocurrency asset you can have and get rich with it. Altcoins can make you poorer and it's not good to store all of them in one wallet like a mixture between good and bad ones.
In security, it's more important to separate them in different wallets. If anything bad from one altcoin project that let my wallet compromised, for example, my bitcoins in another wallet or other wallets will be safe.
Even with bitcoin fund, I would like to store them in some wallets, as who knows if either your desktop computer compromised or laptop or phone. Let's spread your coins to some wallets, you will never lose all of them.