Is 1440p 144Hz better than 4K 60Hz for gaming?

For most gamers, yes. The higher refresh rate makes gameplay feel dramatically smoother. 1440p is still very sharp on a 27-inch monitor.

Do I need a powerful GPU for 1440p 144Hz?

An RTX 4060 or RX 7600 handles 1440p 144Hz in most games at medium-high settings. Competitive games like Valorant run 144+ fps on weaker GPUs.