I think that it’s more even than some may think.
If we’re talking about Shard vs Shard, I have my money on Retribution. His intent doesn’t have the same limitations as Harmony. He will do whatever it takes to win.
One should never underestimate experience on a battlefield. With the Fused, we’re talking about Commanders with thousands of years of experience in war. Humans also have plenty of experience at war. I’d argue that Roshar has a far higher understanding of Military Science. Which means they’ll have a better leadership structure with more disciplined soldiers, civilians are more accustomed to life during a war (and living in a war economy), they’ll be better at responding and adapting to new technologies (and perhaps reverse engineering them), and they’ll be better at running supply lines (and interrupting enemy supply lines).
On the time dilation: Roshar will have ~10 years to prepare for war. I’d expect the Retribution aligned areas will be heavily focused on that. Scadrial will have ~80 years, but their focus will be different. Harmony, as mentioned before is constrained in his ability to act. Kelsier and the Ghostbloods can and will do everything they can do to protect the planet, but Kelsier has fewer resources and less influence than a Shard.
Technology and science in general: Scadrial definitely has the edge here. They have WMDs, lots of aluminum, leechers, and much, much more. But I wouldn’t count Roshar’s science out. They have access to light and anti-light, which are incredibly destructive. Their knowledge of sound and rhythms will certainly help them develop weapons and defenses against allomancy. They also have better access to the Cognitive Realm.
I'd bet on a stalemate that leads to a long, drawn out war. Or Roshar figures out how to destroy a whole planet.