Same problems here. At the start of 1.4, I spent like 2 hours with a journey mode character w/hermes boots, creating large worlds, and running to each side to see if the jungle was covered in evil, cause I wanted a world where the jungle was clean. I did not look for a clean snow biome at all.
I did not get a single world with a clean jungle in those 2 hours (I think this was around 50-60 worlds). I gave up. While this was certainly a frequent occurrence prior to 1.4, it was nowhere near this bad. I could get a clean jungle within 3-7 large worlds before 1.4. Now it is seemingly impossible. Having the world evil on top of the jungle is fine on occasion, as it provides a new sort of challenge, but being practically forced into it is very much a problem.
I suspect having another surface biome (Oasis) to account for in world gen has left the rest of the surface with less space for the other biomes, resulting in the world evil overlapping much more frequently than intended. On a side note, I have also seen many, many less pyramids in world gen compared to before as well, which may or may not be a result of this same scenario, be it intentional or not for regarding pyramids. There were also a surprisingly small number of large worlds that had a natural forest biome outside of spawn that was larger than 50 or so blocks wide. I always make my home base in the not-spawn-forest-biomes, due to my preferences.
I rarely touch mods, but I think I will have to use a mod world gen to force clean jungles in the future if this doesn't get fixed. I know TerraCustom did that, but not sure if it's been updated.