This is very simplistic way of interpreting what Trump said. I would advice to read a bit about the significance of the GIUK (Greenland, Island, UK) in view of warming climate and growing importance of Arctics - melting ice might provide a much better and faster route for trade.

The problem is who will control the entrance and exit to that route and GIKU is one of them. And here we are on the key problem: Denmark for years totally neglected building any security/military infrastructure on Greenland, which suddenly might become a crucial element of the World economy and trade.

Do you really want sadistic regimes like Russia or China to take control over key parts of the potential trade routes (80% of global trade goes through the sees and oceans)?

Whatever you think about Trump, he will be gone in 4 years, someone else can be elected if Trump/Vance fails to deliver. Do you think we can get rid of Putin and his dreams on conquests Europe that easily? Or Xi, who is speeding with extending military potential of China, including nuclear weapons, aircraft carriers? Try to guess why Xi is doing this.