I like rain in NU a lot. Even when I first started playing I found the rain team I was using to be much better than anything else I was using. But ya, with things like Ludi around, as well as the fact that it can abuse two other moves too (which can happen in other tiers as well, but for something like Articuno which can make use of Ice Beam too as well as Hurricane and imo ice can be one of the hardest things to take in the tier at times). Sun I don't think I've really tried much and while it can be really strong to face I just really had no interest to play it. I guess it's probably because I have a preference for using teams with Ludi I guess?
But I wouldn't mind it if gen 6 introduced auto-weather in NU which was ~allowed~ and made Ludi become too powerful for just NU causing it to leave the tier.