NAME some fighters who had smooth, effortless footwork. I'll start off with Alfonso Lopez and Ernesto Marcel.
Obvious guys like Jose Napoles will get a mention. I'll mention Kuniaki Shibata. Brilliant, brilliant feet and movement in general. Incredibly co ordinated as a Boxer and as an athlete. And of course, Fighting Harada has some of the best feet ever IMO. Jack Britton was also said to have had tremendously smooth, clever footwork by description, but unfortunately there's no film of him.
Jose Napoles and Orlando Canizales have mesmerising footwork, in modern times I'd say Lomachenko moves the same as them.
Most of the high level Cuban fighters. That nation is known for putting an emphasis on footwork at an early age and just about all of the top amauter talent from that program have exceptional footwork.