I agree that Christ is the firstfruits of the resurrection harvest.Jesus is the firstfruits of the church.
Not 144,000 jewish men.
That is explicitly stated in 1 Corinthians 15.
But Revelation 14 also explicitly calls the 144,000 "firstfruits unto God and to the Lamb."
Therefore, the question is not whether Christ is the firstfruits of the Church.
The question is why God applies the term "firstfruits" to the 144,000 as well.
Simply saying, "Jesus is the firstfruits of the Church, not 144,000 Jewish men," does not answer that question.
Revelation still uses the term for the 144,000.
So the issue is not whether the 144,000 replace Christ as firstfruits. They obviously do not.
The issue is what the designation "firstfruits" means when applied to them and what harvest, if any, they anticipate.
That conclusion must come from the text, not merely from the fact that Christ is called the firstfruits elsewhere.