Caustic Arrow should still be an okay skill - it was nerfed in 2.1 but has stronger support gems to work with now. But if you want a strong skill to use with that bow - explosive arrow might just be the skill for you. It also scales with gem level like caustic arrow does, did not get nerfed at all, and has good synergy with a bunch of ascendancy classes, including the rather strong Elementalist, and also benefited a lot from a bunch of new and buffed support gems.
As for my feelings about Prophecy League, I'm strangely disappointed, mainly because I came into it with rather high expectations thanks to all of GGG's pre-launch announcements.
I first expected prophecies to be more interesting than perandus packs + boxes - but a lot of them aren't interesting at all, and are more tedious than perandus packs - because you have to travel to past zones and often search for specific mobs to complete them.
I also expected a freely available item economy as GGG mentioned they learned from Perandus that players liked having their build-enabling uniques and such more easily accessible, but Prophecy League is actually quite skewed in what it provides. There's a small subset of specific uniques with prophecies which drop them, and those are all cheap. For example, the Astramentis is the cheapest it's been in ages. But for a lot of useful uniques not on the prophecy drop list - they're back to being expensive again.
Finally, the performance enhancements have were supposed to improve the play experience don't really help at all. If I'm only logging into PoE to trade, then the faster startup/loading time is welcome, but otherwise, the faster startup/loading is exchanged for extremely poor performance for quite some time after zoning - combat can actually become pretty dangerous during this early loading time. GGG actually recently enabled an option for players to disable what was supposed to be the performance enhancing change (asynchronous loading) so that obviously shows that for at least a subset of the players, myself included, it wasn't an improvement at all.
With that said, I still think the game's still very good and a lot better than it was in the past and GGG continues to successfully improve and expand the game most of the time.