Love how made up headcanon that swordsmanship is the best. So why isn't everyone a swrodsman? Why isn't Garp a swordsman?
Because different people are inclined to different fighting styles and Garp was a naturally good brawler, adapting this fighting style that suited him best. Why did majority of top tiers use blades; Roger, Rayleigh, Xebec, Shanks, Mihawk, etc.? Why not just brawling?
The fact Marines undergo training in several areas, including swordsmanship - as seen with Koby in the cover story, yet didn't choose to stick with the blade as he was more proficient in his Rokushiki based fighting style proves my point.