What I know about the DCA method seems a little different from what you are saying. I agree with you that the DCA method can be started at any time provided the capital is read as it is an ongoing investment strategy. I defer with you on the aspect that the DCA method will not be profitable on a bullish market because it can be profitable in any market condition provided the plan is the hold those coins for a long period of time. I also know that the DCA method does not care so much about the price so any time is fine and any price is a fair price for the DCA method.
Maybe everything you said will be appropriate if you are willing to hold for a long enough time, maybe ten years or more, and you have a large enough capital.
But for most investors it is not so simple and they try to make a profit on every bull market so that they can buy Bitcoin again at a cheaper price on a bear market. So small investors try to accelerate their growth, yes it is more difficult and requires quite a lot of knowledge, but you can move faster if you can do it correctly. I do not buy on a bull market, all my purchases I focus on a bear market and it gives me good results.