Carlos Monzon and Alexis Arguello are as slow as can be. Lehlo Ledwaba was by far Manny Pacquiaos fastest opponent, but was the easiest notable fight of his career. A far slower Marquez gave Pacquiao much tougher fights. Tommy Hearns had the fastest hands of the fab 4. But you would struggle to find anybody who rates him over the other 3. Give me timing, good positioning and power all day long. It's very rare to find a great fighter with featherfists. I can think of Pernell Whitaker, Andre Ward and little else. And guys like that have to make it up for it with extreme skill levels. Almost all top level fighters usually hit harder than their opponents. Or at the very least have average power for their weight. The same cant be said of speed. Some excellent fighters have slow hands. We see it all the time.
Spence is a great example for me. He's not slow, but he's not a lightning fast puncher. Just incredible positioning and timing allows him to land so heavy and often.
When somebody thinks it's the most importang thing in boxing, then he is clearly overrating handspeed but it's a great addition to the skillset of an already fundamentally sound fighter and can make a big difference.
It makes a small difference I think. But if the other guy has more power and better positioning then all the handspeed in the world will make little difference.
Generally it makes a small difference but it can make a big difference in certain situations like counterpunching or fighting against a slick opponent who is hard to hit clean but even in that situations things like reaction time and positioning are still more important.
Remember Golvokin vs Monroe Jr. GGG is slow for a top level fighter. And Monroe is a featherfisted slick southpaw. A lot guys going into that fight were saying Monroe would be too slick and push GGG to the limit on the cards. But GGG had FAR more power, timing, and positioning. He cut the ring and timed him. And the fight was extremely easy for him.
Yes, GGG was far superior in almost everything, when things are equal it can make a difference but when you are fighting against a superior boxer it won't help you to win the fight, and when you have fast hands but no power like Amir Khan it doesn't make a difference like it does with someone like Corrie Sanders who overwhelmed his opponents with handspeed but also power which certainly made a difference for him, imagine Corrie Sanders without his handspeed and he wouldn't have been as dangerous anymore.
Getting off on an opponent quicker then they can get off on you is one of the best advantages you can have in the ring. Handspeed is in no way overrated.
I'll take power, timing, punch resistance, stamina, footwork, heart, boxing intelligence, tough skin, nice shorts, boots with tassles on, basically anything over hand speed.
Hand speed is the cherry on the cake, but the cake itself is footwork - which is one key element of to timing imho. No point firing out combos the speed of a humming bird's wings if they hit thin air...