Claiming other people “do not understand much” is rich coming from you, man. Oda’s done some wacky things, but Garp coming to and then dying in Wano would be outrageous even by the author’s standards. Garp’s demise would make Luffy furious, but he doesn’t have the same relationship with his grandfather as he did with his brother. There would be emotional impact, but not one as strong as watching Ace burn to a crisp in his arms. Beyond that, he would be one player of many and counting; Garp is more than capable of holding his own against Big Mom and/or Kaido, and their YCs to a lesser extent, and those are the only enemies who would be able to keep up with HIM more than the other way around. Other people will be occupied with the quasi-Rocks underlings, and others still would also be fighting Linlin/Kaido, so Garp doesn’t even have to be the main player on Luffy’s side.
If Garp needs to die, imo it should be by the Gov. or BB. Garp going down to the very establishment he tried to protect will be lit to see.