As a matter of fact, it's very unsafe to depend on a single coin. In otherwords, invest into more than one token by spreading your investment into potential coins but be careful not to invest into pump and dump coins. Above all, make sure to maintain risk management in which ever crypto asset you are investing in.
IMO no. Spreading your investment don't also guarantee you good profit knowing that most other coins apart from bitcoin are without life span, how about you take out spare money to invest into Bitcoin for a long term investment don't you think it's better than investing in altcoins that may pump and dump as you clearly stated within a short time? Every investment has it's own risk but regardless bitcoin investment has been one of the less risky investment so far especially if you are truly knowledgeable about the investment plan you want to invest and if you made proper findings before investing.
Personally, I have depended on a single coin investment which is bitcoin though the profit has not really been so much but it is far better than losing out funds in altcoins.