The ferocious Ketchel, former MW Champion, who knocked the light heavyweight and kd Jack Johnson, then heavyweight champion at the time, was an ATG, but we never saw him in his prime because he was gunned down at age 24. With his savagery, skill, determination and concussive power, how would he fare vs today's middleweight crowd?
Too crude to win vs top mw's, especially as his style was made for 15-20 round fights. He'd have to completely change to be effective, and who knows if he could adapt to modern boxing.
I would like to drop today's MW's in a time machine to be born in the late 1800's with the diet/training techniques/income/tape/activity levels/gloves of the era Ketchel was raised in, grow up, then fight Ketchel... Whole different ballgame nowadays.
People forget that the biggest aspect in boxing was much tougher back then, the mental one. Ketchel and the fighters of that era, saw their opponents like the person who wanted to put them back on the street again, they where there to fight with all his heart. Not many fighters today can survive that kind of will.