Is Marciano...

Not compared to Joe Joyce,but he certainly wasn't fast, he made up for it by being relentless.

 

His short arms added something to it.

Archie Moor compared it to fighting a propeller .

 

I'd say average or maybe slightly above average for his size. It's more the quantity of punches he threw which is different from pure speed and more about endurance.

 

Something Joyce also used to make up for being slow

 

Marciano did not have great defence,but it was definitely better than Joyce's.

 

Rocky's power punch output was enormous, and his short-reach punches seem to me more like club blows with brutal leverage. He often takes a wide swing for his power punches, though, which I think makes him seem slower.
He doesn't throw smooth combinations like Joe Louis, but the single power punch itself had good speed.

In his fight against Rex Layne, the commentator mentioned that Marciano outspeeds Layne. So he surely wasn't slow. However, boxing fans typically don't compare him to contender-level fighters of his time (like Layne). People compare him to other ATGs. So, of course, the competition is accordingly good (or fast).

 

Sure he did Marciano’s defence was solid, scantly hit clean, Cus’Dmato thought so and Bill Miller thought it was worth Toney studying him.

 

I don’t think he was all that slow. Nothing that stands out. As mentioned though, his output was mind-boggling so even if he missed a few he’d still catch you with a number of others. The speed of them becomes less important when there are THAT many coming at you.

 

Marciano was, but is no longer, and has not been for a long time. Marciano's legacy still is, though.

 

Ancient Louis couldn't miss him with a jab," I just had to take them." Marciano was cut in every major fight he had,he was hard to tag with a big shot but not to hit in general.
Louis, Lastarza, and Moore commented on it. Now you can call me a hater for saying what his opponents remarked upon.

 

Mathews jabbed him at will in the 1st rd of their fight.Second round Rocky left hooked him out of it!

 

Marciano was so green against Louis 4 years in with barely any amateur experience, Louis diminished or not he was formerly the GOAT.

 

Marciano threw with both hands from multiple angles and from a crouch, and he didn't care where he hit you -- arms, throat, top of head -- because he knew it would hurt regardless. However, I'm confident that Ali's speed, toughness, endurance and ABILITY TO INFLICT CUTS would overwhelm Rocky by the late rounds.I can easily see the ring doctor stopping this fight.