Yes, Wesley's ideas on Prevenient Grace were a good antidote for Calvin's Pre-Destination and Election of the Elect.
You can see groups like the LDS and Witnesses as Cults and I agree, from my real life experience attending various Churches I would expand the parameters and include the Calvary groups, Baptists and others. Stand up in a Presbyterian Men's Bible Study group and openly argue against the Westminster Confession sometime and see how welcome you are, or try to take Communion in a Conservative Lutheran church without being a member and going through their catechism.
As to why more JWs are partaking, without them being fully cognizant of the historical underpinnings they are acting out exactely the ideological battle Calvin and Wesley had 500 years ago- Prevenient Grace vs Election of the Elect. the old becomes new and history repeats itself.