Carlos Monzon of course. Roman Gonzalez. Alexis Arguello Joe Frazier Vicente Saldivar Eder Jofre could also start slow.
Salvador Sanchez is another one who was sometimes slow out the blocks. Not against Gomez or Lopez however.
One not mentioned: Rodrigo Valdez. While he was under Gil Clancy's tutorage, he often cautioned the refs against any bias against 'Rocky's' early passivity. And...when he let go?...Boom