If they are no peaks then Luffy would never catch up. I get its a manga and Oda can do watever he wants, but Oda won't have WB at age 130 still improving his techniques.(i am pretty sure of that)
Just because you have room to improve doesn't mean you will, Oda can simply have WB stop increasing his power because he fears what he might become or some bullshit, simple.
And if Buggy ate Luffy's fruit he would be different because Luffy is different from him physically and mentally.