Christianity as such will be the dominant ideological force by c. 400 as in OTL,but its path to victory and the extent of its suppression of the 'pagan' faiths will be substantially reduced. How and why will be explored by some smalle,r some larger alterations from what really happened. Not so much with Constantine, though I am tweaking his career from time to time, but a greater and longer role for Julian... which will reduce the room for manoevure of later authoritarians like Theodosius.
I have been struck ever since first reading up the history of this era , aged about 14, how aggressive and brutal the Church - and its bands of 'stormtrooper' style militant monks and Church admin 'hangers on' could be, not at all 'meek and mild' Christianity as we think of it but rioting and wrecking, and decided this all needed a bit of rederessing. The 'smash up the unholy past' activities of certain C4th Church leaders have an air of the Cultural Revolution about them, which I was surprised has not been remarked on until recently - but then when I talked to potential supervisors at London Univ as a postgrad student about doing a higher degree on the 'relevance' of iconic historic events to modern politics as pointing out useful parallels and showing a common pattern of events, specifically Cromwell's religious radicals and regicides in the 1640s-50s as a parallel to the theocratic Iranian Revolution , they were horrified at the idea!