Basically Bitcoin needs plan. And in my point of view anyone has Bitcoin or he is buying with DCA method so I think he should never sell all the Bitcoins at once. He always hold some amount of Bitcoins. And if anyone will believe on Bitcoin and will Hold for 4-10 years or even more so definitely Bitcoin will give benifits of his/her believing.
It's not a guarantee that hodling bitcoin for years will prevent its price from falling to a point where it's affordable to purchase during a bear market since the bear market serves as an opportunity to buy Bitcoin at a low price.
I agree with you that holding Bitcoin for years will not prevent the price of Bitcoin from not falling, but hodling Bitcoin for years will play an important role in your Bitcoin hodling because there will be a time when Bitcoin price will never fall below $50k, and if you are still hodling your Bitcoin till that time you will not have to buy Bitcoin on a high price. But if you sell your Bitcoin before that time and you want to buy it again, you will have to spend a good fortune before you can accumulate a reasonable quantity of Bitcoin because the price of Bitcoin will be excessively high.