Yes it is:
Rev 13:15 And he had power to give life unto the image of the beast, that the image of the beast should both speak, and cause that as many as would not worship the image of the beast should be killed.
Rev 13:16 And he causeth all, both small and great, rich and poor, free and bond, to receive a mark in their right hand, or in their foreheads:
Rev 13:17
And that no man might buy or sell, save he that had the mark, or the name of the beast, or the number of his name.
Not a word about the Sabbath or Sundays or worshiping. Yes, those who take the mark will worship the beast also but the mark is specifically about buying and selling. It's I.D. that says someone can buy or sell things.
The Antichrist and the Great Tribulation have not happened yet so no, it wasn't fulfilled by the RCC.
Not all beasts are kingdoms. The false prophet is a person, one person. He will be a ruler of a beast kingdom though.
A beast has also been used to represent a person or persons (beasts) and that hasn't changed either:
Ecclesiastes 3:18 I said in mine heart concerning the estate of
the sons of men, that God might manifest them, and
that they might see that they themselves are beasts.
Titus 1:12 One of themselves, even a prophet of their own, said,
The Cretians are alway liars, evil beasts, slow bellies.
2 Peter 2:12 But these,
as natural brute beasts, made to be taken and destroyed, speak evil of the things that they understand not; and shall utterly perish in their own corruption;
Jude 1:10 But these speak evil of those things which they know not: but what they know naturally,
as brute beasts, in those things they corrupt themselves.
Spiritual Mark and Seal
We both agree, the Seal of God is a spiritual mark.
2 Timothy 2:19 Nevertheless the foundation of God standeth sure, having this seal, The Lord knoweth them that are his. And, let every one that nameth the name of Christ depart from iniquity.
Angels are tasked with giving the Seal to the servants of God.
Revelation 7:2-3 And I saw another angel ascending from the east, having the seal of the living God: and he cried with a loud voice to the four angels, to whom it was given to hurt the earth and the sea, Saying, Hurt not the earth, neither the sea, nor the trees, till we have sealed the servants of our God in their foreheads.
Both of the mark and the Seal are given by angels, not men, therefore it can't be an I.D. or anything physical. Note that they
receive the mark of the beast, pointing to action of a spiritual nature. God
marked Cain so that he wouldn't be killed.
As for buy and sell, yes, I know the verses well, I just didn't quote them in my post. The mark and the seal are both spiritual marks that show who you worship.
Worship
Five verses in Revelation mention worship and the mark of the beast. Since you didn't see it the first time, I'll quote it again.
Revelation 14:9
And the third angel followed them, saying with a loud voice,
If any man worship the beast and his image, and receive his mark in his forehead, or in his hand,
Revelation 14:11
And the smoke of their torment ascendeth up for ever and ever:
and they have no rest day nor night,
who worship the beast and his image, and whosoever receiveth the mark of his name.
Revelation 16:2
And the first went, and poured out his vial upon the earth; and there fell a noisome and grievous sore upon the men
which had the mark of the beast, and upon them which worshipped his image.
Revelation 19:20
And the beast was taken, and with him the false prophet that wrought miracles before him, with which he deceived
them that had received the mark of the beast, and them that worshipped his image. These both were cast alive into a lake of fire burning with brimstone.
Revelation 20:4
And I saw thrones, and they sat upon them, and judgment was given unto them: and I saw the souls of them that were beheaded for the witness of Jesus, and for the word of God, and which had not
worshipped the beast, neither his image, neither had
received his mark upon their foreheads, or in their hands; and they lived and reigned with Christ a thousand years.
If, for instance, Sunday worship is enforced, the powers that be don't need an I.D. to determine whether you're worshiping on Sunday or not. Church attendance, or lack thereof, will be readily apparent and reported to the authorities, limiting your ability to buy and sell.
The Beast
Daniel 7 and Revelation 13 are speaking of the same beast (spiritual Babylon), of the same origin—the first four kingdoms of the earth (Babylon, Medo-Persia, Greece and Rome).
Daniel 7:4-8 The first was like a lion, and had eagle's wings: I beheld till the wings thereof were plucked, and it was lifted up from the earth, and made stand upon the feet as a man, and a man's heart was given to it. And behold another beast, a second, like to a bear, and it raised up itself on one side, and it had three ribs in the mouth of it between the teeth of it: and they said thus unto it, Arise, devour much flesh. After this I beheld, and lo another, like a leopard, which had upon the back of it four wings of a fowl; the beast had also four heads; and dominion was given to it. After this I saw in the night visions, and behold a fourth beast, dreadful and terrible, and strong exceedingly; and it had great iron teeth: it devoured and brake in pieces, and stamped the residue with the feet of it: and it was diverse from all the beasts that were before it; and it had ten horns.
Daniel 7:23 Thus he said, The fourth beast shall be the fourth kingdom upon earth, which shall be diverse from all kingdoms, and shall devour the whole earth, and shall tread it down, and break it in pieces.
Revelation 13:2 And the beast which I saw was like unto a leopard, and his feet were as the feet of a bear, and his mouth as the mouth of a lion: and the dragon gave him his power, and his seat, and great authority.
The book of Daniel was sealed until the time of the end, so that Revelation could be understood at the appropriate time (Daniel 12:4-9, Revelation 10:9-10).
Nothing says we have to agree. I've stated my position and you've stated yours.