I think the math might be off a bit for Person B. After selling the first bitcoin, he has $4000 ($2000 profit). When he buys back in at $2500, he has $1500 cash and 1 bitcoin worth $2500 (1.6 bitcoin total worth, as you noted). When the price reaches $4500, he sells and now has $6000 cash, or 1.33 bitcoin total worth ($4000 profit, since the coins he bought appreciated $2k both times he owned them).

But you are right that participating is where you make the most. You make profit on many of the swings up and down. Whereas the person that just holds and doesn't trade makes profit only on the overall upswing, and not on any of the dips and repeat upswings.

Person B makes 60% more profit than Person A ($4000 vs $2500). And that is figuring in just a couple trades. The difference could be much much more with many trades.

It does help understanding trading to break it down into simple examples like this, and why it is important to sell at the tips, and then wait for the dips to buy back in again.