The comic that had the two fighting each other basically showed that each had inherent weaknesses (their strengths were basically the same since Echo was able to replicate anything DD did due to her being a memory mimic. To be honest with you, she was even better than he was in terms of abilities since she not only PERFECTLY mimicked him, but also did the same to Bruce Lee, BullsEye, and a number of others).
It is in weaknesses where the real differences are, and the comic actually showed how each character could capitalize on them. Echo, after knowing about DD's senses, basically blocked them out and proceeded to almost kill the man (his senses were overloaded). DD, after knowing about her over-reliance on sight, basically did the same by fighting in a dark area where her sight was useless (and being deaf she couldn't even hear).
Thus the fight is at it was in the book ....it depends on who capitalizes on the other's weaknesses. Because, in terms of strength, it would be like DD fighting himself (with a slight advantage to him since he is stronger physically, and a slight advantage to her since she is not only aping DD but also a host of other people).
It boils down to who uses the weaknesses of the other against them.
One thing that wasnt mentioned by Spet was that Echo was Bloodlusted, whereas DD didnt want to hurt her and was just trying to talk to her as well as stopping her, but she never stopped to actually read his lips. Also, that was their first encounter. If they were to fight now, shed be predictable in a way making it even harder for her to get a victory.