Please educate me on the topic

I heard that Emmanuel Steward was the man who made them popular

Did Sugar Ray Robinson, Ali, Sugar Ray Leonard, Duran do mitts when they were learning boxing? I saw Hagler hitting big gloves of his coach, sort of mitts, Tyson did whem with Rooney.

I personally believe they are good when polishing a fighter with good fundamentals, but they are overrated when teaching these fundamentals, especially if the coach is not an expert.

What do ya think?