Thunder

If I remember right, in P3 Thunder II added effect Thunder II, and Thunder added effect Thunder. They stacked.
Now, Thunder II adds effect Thunder instead of Thunder II. It doesn't stuck and just renews previous one.
DoT from both skills Thunder and Thunder II is same for some reason now which doesn't make any sense to me tbh. Since that eliminates point of Thunder II as whole (well, not really as whole, but pretty much). I mean, why would you need another DoT skill which does same DoT as lower one and doesn't stuck with it.

Uhm, I'd really like some clarification on this. Is this intended (which I doubt) or is indeed bug?

Yeah, it seems pretty pointless to have a longer cast time, 10 more normal potency and the same DOT potency. Thunder 3 looks no better, if you look ahead in your skill book.