A pure boxer IMO is someone who doesn't clinch,doesn't run and uses his skills and is equally adapt at offense and defense I think lomachenko is the best pure boxer I'd add Gonzalez,rigo(when he wants too) GGG,canelo,
I outlined what I consider a pure boxer. A guy with great offensive and defensive skills, I don't consider runners and huggers with limited offense pure boxers becusee they only excel in one aspect of the sport ,defense. It would be the eqiuvlent of calling a face first brawler like ruslan a pure boxer
Based on the above explanation, Lomachenko, Gonzalez, Usyk, Crawford and Golovkin are the names that spring to mind for me.