I commend you for voicing this opinion and disagree with you with every fiber of my being.
Why introduce astral projection instead of having Luke become one with the Force and then stall Kylo? The outcome is the same, but it doesn’t require the introduction of a new Force power and doesn’t imply that Luke used up his life force or whatever, which is also a completely new thing in the Star Wars universe. Having Luke’s Force ghost instead aligns with Episode IV when Obi Wan says that when he joins the Force he’ll be more powerful than Vader can possibly imagine.