If the fulfillment of God's promises are just "Christianity will be the most popular religion in an ongoing sin corrupted fallen world until the heat death of the universe" then God is disappointing and impotent, using grandiose language for very mundane things.
What are you talking about?! I do not think you really understand the purpose and plan God has for His Church on Earth. We had a great commission since the Pentecost that God empowered us with the Holy Spirit to preach the Gospel to the rest of the world then the end will come. It is not about making "Christianity" popular religion at all! Because it is not!
Mat 24:13-14
(13) But he that shall endure unto the end, the same shall be saved.
(14) And this gospel of the kingdom shall be preached in all the world for a witness unto all nations; and then shall the end come.
Our job is to preach Gospel until God see that we have secured all of the Elect He intended to be seal has been sealed, THEN the time of the end come including the apostasy of the church and the judgment of the harlot prior to Second Coming.
Rev 7:1-3
(1) And after these things I saw four angels standing on the four corners of the earth, holding the four winds of the earth, that the wind should not blow on the earth, nor on the sea, nor on any tree.
(2) 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,
(3) Saying,
Hurt not the earth, neither the sea, nor the trees, till we have sealed the servants of our God in their foreheads.
Christ has bound Satan so he could build His Church through His witnesses who got the great commission from God to do this! He seals (saves) people through our witnesses! After we have secured the last elect (only God knows), THEN the end will come. That will be when the church starts to slide into apostasy and desolation when the day of salvation actually over! at leasT for a short season! That is why the number of "alive and remain" Elects are getting smaller and smaller as the "short season" proceeds. There will NOT be very many faithful church on Earth when Christ returns!
Luk 18:8
(8) I tell you that he will avenge them speedily.
Nevertheless when the Son of man cometh, shall he find faith on the earth?
So do you honestly think Christianity is going to be a popular religion today, humm?