Corypheus' plan; breach the veil, enter the fade. Corypheus' goal; become a god, restore Tevinter.
Solas' plan: tear down the viel, open the fade. Solas' goal; kill the false gods, restore the ancient elves.
Drastically different, these two.
At the risk of sounding like a bit too much of a free-loving hippy, here's my crazy take.
Yes, Corypheus and Solas are two sides of the same coin. Most folks either see Cory as a soulless monster and see Solas as a reluctant, redeemable monster or see them both as soulless monsters that they want to murderknife. After Trespasser I'm in neither of these camps. All those parallels we can draw between Solas and Corypheus actually make me feel some sympathy for Corypheus rather than hatred for Solas. He, like Solas, is a Rip Van Winkle who rose from a long nap into an alien world--a world he intended to fix. Perhaps if Cory had had someone to slap him in the face or to shake him by his nasty darkspawn shoulders he could have been redeemed. He could have chosen a different path. Perhaps he could have been more like the Architect. Monsters are not born in a vacuum, and every soul is worthy of redemption.
Redemption is a recurring theme in Inquisition. What did all you Solas knifermurderers make of Blackwall? Did you leave him to hang? Send him to the Wardens? My Inquisitor allowed him the opportunity to atone for his crimes. She also showed mercy to Alexius and Florianne, allowing them to seek redemption in the service of the Inquisition.
Seeing the people of modern Thedas as somehow superior or more deserving of protection than the ancient elves is ethnocentric. Both groups have the right to live. One who is violently angry at Solas for plotting to potentially destroy the world should be just as angry at him for destroying his own world in the distant past (and subsequently becoming the unknowing creator of modern Thedas). I don't hear any of you complaining about that. Solas has killed more people (generations of elves who died through their own mortality) as a result of creating the veil than he is likely to kill by sundering the veil. Kill a bunch of people all at once to prevent perpetual death in the future. Every time an elf dies of old age it is Solas' fault--collateral damage from his Big Magic 1.0© plan.
Again, this is just my crazy hippy opinion.