Nah, The Gospel Apostle Paul preached is the same... Gospel that Christ's other Apostles preached. What those on men's Hyper-Dispensationalist movement have done is succumbed to a certain group of men who have created false traditions by fabricating a Scripture interpretation that is 'outside' God's Word.
Per the Book of Acts, and Paul's Epistles, Paul preached the Kingdom Gospel:
Acts 14:19-22; Acts 19:6-8; Acts 20:16-25; Acts 28:23; Acts 28:30-31; Romans 14:14; 1 Corinthians 4:19; 1 Corinthians 6:9-10; 1 Corinthians 15:24; 1 Corinthians 15:50; Galatians 5:21; Ephesians 5:5; Colossians 4:11; 1 Thessalonians 2:12; 2 Thessalonians 1:5.
The "mystery" tradition from men being pointing to in the OP is nothing but an idea from a certain group of men that try and isolate something Apostle Paul said in the following Scripture, and then attempt to create a whole new doctrine out of it that does not exist...
Rom 16:25-26
25 Now to Him That is of power to stablish you according to my gospel, and the preaching of Jesus Christ, according to the revelation of the mystery, which was kept secret since the world began,
26 But now is made manifest, and by the scriptures of the prophets, according to the commandment of the everlasting God, made known to all nations for the obedience of faith:
KJV
Those men try and isolate that "my gospel" phrase as IF Paul was claiming a different Gospel than what the Apostles preached. That simply is not so, Paul preached the same Gospel of Jesus Christ that they preached, for there is only ONE Gospel of Jesus Christ.
Also, those men totally disregard that above "and by the scriptures of the prophets" phrase of Paul pointing to one of the sources... of the Gospel that he preached!
Paul didn't cover in that above Scripture that point about the Old Testament prophets having a part in that Gospel, but Paul does cover that point elsewhere in his Epistles.
And note to whom Jesus would choose Apostle Paul to take The Gospel to...
Lord Jesus said about Paul:
Acts 9:15
15 But the Lord said unto him, "Go thy way: for he is a chosen vessel unto Me, to bear My name before the Gentiles, and kings, and the children of Israel:"
KJV
Thus Lord Jesus sent Apostle Paul to preach The one Gospel not only to Gentiles, but ALSO to the kings, and to the children of Israel! By that common sense ought to tell you easily that Lord Jesus sent Paul to preach the same Gospel to all three above groups.
Men's Hyper-Dispensationalist movement, is where those false ideas come from that try to claim that Paul preached another Gospel different than the Apostles. (also called Hyper-Grace movement.) They pack all sorts of teachings about 'grace' with it to trick the Biblically unlearned, just like they also do with man's false pre-trib rapture theory, which many of them also push.
Here is another Scripture example by Apostle Paul that they abuse, taking it out of its context...
Eph 3:1-6
3 For this cause I Paul, the prisoner of Jesus Christ for you Gentiles,
2 If ye have heard of the dispensation of the grace of God which is given me to youward:
3 How that by revelation he made known unto me the mystery; (as I wrote afore in few words,
4 Whereby, when ye read, ye may understand my knowledge in the mystery of Christ)
5 Which in other ages was not made known unto the sons of men, as it is now revealed unto his holy apostles and prophets by the Spirit;
6 That the Gentiles should be fellowheirs, and of the same body, and partakers of his promise in Christ by the gospel:
KJV
Do you see what Paul said above about the "mystery" with that, "as it is now revealed unto His holy apostles and prophets by the Spirit"? Paul showed right there that to the other Apostles the "mystery" was ALSO REVEALED TO THEM. And what is the "mystery"??
Verse 6 above tells us; it is that Christ's Salvation would go to the Gentiles who believe also. In Old Testament times, that was not understood by God's prophets...
Did you not know brethren, that Apostle Peter taught about this "mystery" that Paul mentioned in his Epistles? and Peter showed how the Old Testament prophets who prophesied about it, searched the Scriptures about it, as they didn't yet understand it...
1 Peter 1:9-12
9 Receiving the end of your faith, even the salvation of your souls.
10 Of which salvation the prophets have inquired and searched diligently, who prophesied of the grace that should come unto you:
11 Searching what, or what manner of time the Spirit of Christ which was in them did signify, when it testified beforehand the sufferings of Christ, and the glory that should follow.
12 Unto whom it was revealed, that not unto themselves, but unto us they did minister the things, which are now reported unto you by them that have preached the gospel unto you with the Holy Ghost sent down from heaven; which things the angels desire to look into.
KJV
Brethren in Christ, do you even read... your Old Testament Books of God's prophets? Did you not know that God's prophet Isaiah was given to prophesy about Christ's crucifixion? (see Isaiah 53) And king David, who also was a called prophet of God, he also prophesied about Christ's crucifixion (See Psalms 22).
Thus it's like those men who came up with the Hyper-Dispensationalist, a.k.a. Hyper-Grace movement, failed to even read those Old Testament prophet witnesses about Christ's crucifixion, and then simply attempted to claim Apostle Paul was the only one it was revealed to. No, the "mystery" was revealed by God through His Old Testament prophets first, yet they didn't understand it when it was revealed to them. It would require Christ's actual 1st coming to die on the cross in order to openly reveal it, and Christ's Apostles, all of them, it was revealed to, not just Paul only.
If you want to learn the places in The Old Testament prophets where Christ's Salvation would also go to the Gentiles... here is a start. The Book of Isaiah has probably the most OT Bible prophecy about it, as the name Isaiah means 'Yah is Salvation': Isaiah 11:10; Isaiah 42:1-6; Isaiah 49:6; Isaiah 49:22; Isaiah 54:3; Isaiah 60:3-5; Isaiah 60:11; Isaiah 62:1-2.