Somewhat similar fighters but too me Charles was more of a counter puncher that could also bang and Holyfield was a boxer puncher that liked to trade. I think Charles was the more technical fighter and Holyfield was more aggressive in nature. Both were tougher than a 2 dollar steak.
Both fights could amaze or confound crowds. Both intellectually their best strengths and weaknesses. Both were known more for their willingness to push themselves to reach their peaks, but could make mistakes due to pride. Holyfield could fight very intelligently though Charles may have had the better ring IQ. Charles was a slight heavyweight even in his day, Holyfield benefited from modern training and science (no snide remarks) to become a bit more heavyweight. Both clearly trained their inner selves for bravery rarely seen. Charles had to be more the matador, though he was not without snap in his punches. Holyfield pack a bit more gun to the gunfight.
I don't think they were especially similar, beyond being small HWs for their time. At LHW Charles was a supremely talented boxer puncher, the closest to a LHW sized SRR I can imagine. After killing an opponent and against larger fighters at HW, Charles fought far more cautiously as a pure hit and move boxer. I don't think Holyfield was as physically talented (though he was still immensely so) and whilst he could box, he was more attritional, relying on his incredible chin, physical strength, stamina and toughness.