Aww that sucks Ite, i've missed the December part 2 ones because I didn't complete one of the missions and I hated that I'd forgotten it and missed out on books and tickets.
Zidane is absolutely still relevant, in Lufenia content I've ran him more than I ran the twins before Machina came into play because while the Twins bring nutty damage with their LD and BT effects, Zidane brings utility.
I used Machina a lot lately because I knew how much damage he could bring to end fights quickly, worth noting you can use more than 1 BT finisher move in the party just not the full rotation so I've paired him with Machina although sometimes doesn't work because his followups can steal Zidane's breaks but they do work very nicely together if I want to delete turns to bring Machina back faster but I run them separate a lot.
We are in a period now where the orbs are non fatal, c90 is bringing old units back up to scratch and giving them life again and the Lufenia fights are more straight forward without crappy strict mechanics so I'm going back to Zidane as my main for a little bit because he brings a lot of utility and still a lot of damage.
My favourite thing I ever used him with was a party comp with Iroha, her abilities allow you to hold brave damage and after using Zidane's finisher he had a 500k brave surplus in hold which immediate got fired into the enemy, had never seen anything like it.
Locke is up next on my list his kit is a little complicated to get the most damage out if him but I'll learn the rotation and he also brings heals i've a BT book and 3 ingots waiting for him and i'm ready to realize his high armor.
I don't know what to expect for the anni but can't wait for the stream.
Just read on what JP is getting for their 5th anni, lots of really cool changes I forgot theirs runs same time as ours I can't wait til we get that stuff next year!