You are right, however I believe that some people prefer not to invest all of their money at once without thinking about market conditions first. Sure, a lump sum means you invest everything all at once, but not everyone is comfortable with that. Many people choose to wait for a better price before investing their money, because no one wants to buy when the market is too high.
So, buying the dip and lump sum are not the same thing, it's just that people do their things differently. Some may decide to invest their money once, while others will wait for a dip. But, in the end, it will depends on how the person thinks and the kind of risk they are willing to take.
What is the best price quoted by the Bitcoin guy? Do those who actually wait to buy Bitcoin at DIP really find the DIP price? For example, suppose when the price of Bitcoin was $60,000, a person planned to invest in Bitcoin but not at this price, he would start buying when the price drops. But when the price of Bitcoin reached $40,000, it was found that he was still not investing, when he was asked why he was not buying now that the DIP price was higher than the previous price? His answer would be that he wanted to wait for more DIP. Again he waited for a while and it was found that the price of Bitcoin had dropped to $20,000 and this time he still did not invest in Bitcoin, again he was asked why he was not buying Bitcoin. He said that Bitcoin had reached $60,000 to $20,000 and its price would drop further. Along with this, many other thoughts came to his mind as to whether Bitcoin is actually a real asset. That's why he couldn't invest even after it reached $60,000 to $20,000. He wanted to wait more, but later it turned out that its price had increased to $30,000. He then said, "I got it for $20,000, I didn't buy it. Now the price is high, and when the price of Bitcoin drops, I will invest here."
To be honest, this is the reality for those who wait for DIP to invest in Bitcoin. They don't actually find the real DIP, so they can't invest
and later regret it.
What I tell fellow Bitcoin investors when we are having chats is that we should buy when we have available funds for it. No need to wait for it to dip before buying because you don't control it's price, it is a volatile asset that can swing up or down without notice. If you believe that Bitcoin can always reach ATH in every bull circles that should be your focus because at any price that you buy you'd always be in sure profit when another ATH happens.
This is why it's important to think long term if you want to have sure ROI in Bitcoin investment. Have a solid plan for it, either it's DCA method or buying in lump sum let the goal be to hodl for a long term between 8 to 10 years and beyond.