It depends how you invest in Bitcoin. If you only buy the coins you have the risk loosing money. There are derivatives strategies on BTC so that you can always make money. It is a zero risk construction.
Their are so many different constructions to make from zero risk till high risk, it depends how you want to invest in it.
Invest in BTC with no underlying strategy is pure gambling.
Buying bitcoin for long term investment is not risky, the risky behind it is where you save the bitcoin. If you buy in centralized exchange and leave them there, you are risking your money with exchanges that may go bankrupt or get hacked anytime.
Buying altcoin is more riskier than bitcoin. You don’t need any strategy to buy and hold bitcoin I don’t know why you are saying that investing without any strategy is gambling.