I suppose it depends what one means by "the Gospel". The phrase is often used to refer to the invitation to sinners to come to God through Christ and receive forgiveness and new life, and ultimately glorifucation. But the phrase can also be used to denote the whole of the Christian revelation. I would prefer to say, not that "Calvinism is a distortion of the Gospel", but rather that it contains the Gospel but leaves a lot out. Here in Wales most revivals have been led by Calvinists, from the 18th century onwards, though not (I think) the 1904-5 awakening. In England, the side of the 18th century awakening led by George Whitefield and his associates was Calvinistic. Scotland has been thoroughly Calvinist. God was pleased to use those preachers, and those movements, as channels to bring many sinners to Christ, who now (I have no doubt) are in Paradise with Christ, awaiting the resurrection of the just. But (in my personal view) Calvinism goes wrong in two ways: (1) it leaves out other truths, such as that Christ died for all, that God extends a sincere invitation to all mankind to come in repentance and Christian faith, and that that call of grace can be resisted; and (2) it seeks to answer questions God has not answered, and has created a logical, philosophical sealed system with no loose ends and no mystery.
I also feel (and many on this forum will disagree) that we all distort the Gospel. I think we Evangelicals under-emphasise the resurrection of Christ (and of the believer), whilst focusing almost exclusively on Christ's redemptive death and the forgiveness of sins committed. But my reading of Orthodoxy leads me to the conviction that Orthodoxy concentrates on the resurrrection to the extent of under-emphasising the Atonement achieved at Calvary. One could give other examples, but the point is made.