P1 is false, P2 is false, P3 is false, and unsurprisingly C1 and C2 are false.
Continuationists do not claim canonical revelation.
Continuationists acknowledge no new canon has appeared since the Bible.
The Bible does not say that prophecy and revelation are usually canonical, let alone necessarily canonical. If the only purpose of revelation was the canon, non-canonical prophecy wouldn’t have been going on. P1 is false. (It may be possible to complicate this point, but not change the result. If one claims “special” revelation is by definition canonical, then the statement is vacuously true, but with those definitions it would just mean that the revelation still happening is not “special”. Take care with this definition and argument. In no case can it be claimed that revelation and prophecy in general are canonical, and that’s what matters.)
Signs were so ubiquitous that it’s unreasonable to claim they were only for authentication of authorship of the Bible. I also doubt there is any good case that scripture claims “God only gives sign gifts to His servants/apostles to authenticate their authority as conveyors of inspired messages intended to become part of the Biblical canon.” P2 is false.
(1-3 is enough to make it irrelevant. But on top of all that, I’m almost positive that the Bible never says the canon is closed. P3 is false.)
Conclusion and Support
The idea that assembling the canon is going to be one’s cut-off point should not be conflated with the idea that a closed canon is itself evidence of cessationism.
The Bible contains dozens if not scores of descriptions of non-canonical prophecy.
1 Samuel 19:20
King James Bible
And Saul sent messengers to take David: and when they saw the company of the prophets prophesying, and Samuel standing as appointed over them, the Spirit of God was upon the messengers of Saul, and they also prophesied.
Numbers 11:26 KJV
But there remained two of the men in the camp, the name of the one was Eldad, and the name of the other Medad: and the spirit rested upon them; and they were of them that were written, but went not out unto the tabernacle: and they prophesied in the camp.
1 Peter 1:10-12 KJV
10 Of which salvation the prophets have enquired and searched diligently, who prophesied of the grace that should come unto you:
I could go on. Paul seems to describe a state where every new church is prophesizing, including many individual members of each, very little of which was recorded.
One Possible Root of the Issue
It’s almost as if they claim God intervenes in His universe, enters the hearts and minds and bodies of His followers, heals the sick, saves the world, resurrects the dead.. so we would believe the Bible. Bibliolatry may be involved here. The book is great, but we need to know the author. The Logas of God, translated “The Word of God” is not a document. The Word of God is the Second Person of the Trinity. The words of God, the spirit-breathed divine scriptures, are important, but translating “The Logas”, which is Christ, as “The Word”, and then accidentally confusing that sometimes with scripture... all of that is the background story here. Faith in Christ saves. Not faith in the Bible. Of course they cannot be separated, but a saving relationship with the actual Divine True God (The Logas) doesn’t come solely from a book, or knowledge, without a surrendered heart.
We are clothed and counted as righteous through faith in The Living Christ.