You are absolutely correct, it is very hard or rare to see Bitcoin drop 50% and I don't think it can ever happen unless Bitcoin has lost it potential and some altcoins don't even have potential I mean some of them or if not all depends on Bitcoin because increase in Bitcoin price will result to increase in those altcoins price and decrease in Bitcoin price will also result to decrease in those altcoins price. But I disagree with your last statement that "trading Bitcoin is always safer" that is not true because whenever you trade Bitcoin the chance of you making loss is very high perhaps the safest way to go about Bitcoin is buy investing in it ( buying and holding for a long period of time).
I think bitcoin has dropped 50% more but it didn't happen all at once but several corrections. But isn't a decline an opportunity to buy more aggressively and often it happens but we are still afraid to press the buy button.
Historically, bitcoin has managed to record ath and ath so an investor who dares to buy when the decline occurs is the lucky one like in the case of ftx and luna where at that time bitcoin touched a price of $15k and this year it rose to $108k.
With this history, of course, long-term investment is an opportunity to get big profits. But that doesn't happen in the near future but we have to be patient while accumulating bitcoin. Investing in bitcoin requires a lot of patience because without patience you will not achieve satisfaction to see new highs in the years to come.