I think there are a number of things that would have increased the performance of Odium's forces in the past
(1) More sane Fused. Both in terms of numbers, as well as individual sanity.
(2) Thunderclasts. From the wiki: "They were powerful enough to pose dangers even to the Heralds, with Kelek in particular dying to them several times". So far they have been mostly absent
(3) The Singers hadn't spent the last few thousand years in slaveform. A warform Singer probably has an advantage over a human soldier given equal training and weapons. A warform singer also has built in armor.
(4) More Regals. Humans might have the advantage in topline strength with the Knights Radiant. But Odium would have the advantage in numbers of mid-tier troops.
(5) Gemstones. Necessary for holding stormlight. Maybe gemstones were less common, or less well cut, so Radiants had to be more careful of using stormlight in battle.
(6) Overrating of Knights Radiant combat abilities. Windrunners are one of the top fighting orders, and Kaladin was basically a prodigy even before becoming a Radiant. Jasnah, even at the 4th oath, was not as impressive.
(7) Ba-Ado-Mishram: Powerful enough to basically power a desolation on her own. Currently imprisoned. What did she do during the desolations?
(8) Increased human technology. Bottom line human soldiers probably have better weapons and armor. See point 3.
(9) No shardbearers.
So in summary. Odium probably had better lower end and mid-tier troops. While humans would probably had better higher end troops with the Heralds and upper-oath Knights Radiant.