The rumble balls have a time limit tho. He'd just pop back to normal size eventually and sink the ship lol
As of now! Keep in mind the Rumble Balls were Chopper's own creation with limited resources. Caesar was able to amplify the effect of the Rumble Balls after studying them for a short time, and we know how much better Vegapunk is at science than the man who had Gifters growing ass-roosters.
Chopper can't do it on his own, but Lilith + Chopper with Ancient Elbaph tech/knowledge? I can see them making legit shrinking tech. Would be HILARIOUS after all the Ant-Man/Thanos and Chopper/Kaido theories, if Chopper makes the One Piece equivalent of shrinking tech.
The WG and people like Big Mom have sought the ability to become Giant, and have that power, for years.
Harald is the other side of things: IMO, a Dream of many Ancient Giants, was to be able to shrink, and live amongst humans on the same level.
If the theory about Lilith/Chopper making Shirking Drugs comes true, I think it will be by researching Ancient Elbaph tech created by Giants who wanted to be able to shrink down and interact with smaller-races. Even Kong gets into this when Garp/Tsuru/Sengoku were arguing with him.
Chopper making a drug that lets Gyaban hold Ripley and Colon in his arms is actually really touching to me.