The phrase "are so copious" is correct and usable in written English.
It can be used to describe something that is abundant or plentiful, often in reference to quantities or amounts.
Example: "The notes from the lecture are so copious that I struggled to keep up with the information being presented."
Alternatives: "are so abundant" or "are so plentiful".
Since main courses are so copious, one is advised to go lightly on starters.
It's not pop music but Wainwright's gifts are so copious, perhaps he should stop trying to fit in and simply revel in his uniqueness.
Indeed, the very scholar whose uncompleted notes constitute the bulk of the book's literary references, which are so copious and catholic it seems ridiculous to try to provide even a suggestion of their scope.
The king cobra's paralyzing venom is so copious and powerful that elephants have died within three hours of a bite to the toe or trunk.
When his father was alive, he said, the rice harvest from their fields was so copious that the leftover straw covered more than a hectare, about three acres, of land.
But the connections between the Trump campaign and Russia were so copious that it would be positively bizarre for there not to be a serious, thorough investigation, especially considering that we know Russia carried out a comprehensive effort to manipulate our election.
A new wave of bars is revolutionising Sydney's nightlife scene, meaning that entertainment in Australia's largest city has never before been so copious, lively or accessible.
Because those metals are so hot (around 10 million degrees), they emit copious X-rays.
And yet, like Newcomen, their innovations are so much more useful to the people who actually have copious amounts of raw material to work from.
The English (who traversed the globe as the "British") encountered, and fought, and defeated, more foreign peoples than any other European imperial power; so it stands to reason that their vocabulary of ethnic contempt should be so much more copious than, say, that of the French or the Spanish.
"Our farts were so smelly after the copious meal, we nearly suffocated," he told the Telegraph.
