Giratina-A behind Screens.
...Now tell me how you feel about it.
Zama was barely kept OU cause it doesn't have enough tools to take advantage of its stats, it has overtuned stats across the board and I really despise the increased speed creep that's been happening over the years to the point base 100 without a scarf feels slow now, but regardless zama doesn't take full advantage out of its stats especially with its lack of recovery and mostly being a physical wall. I still ain't sold its healthy in the tier but its here so have to live with it, its mostly the speed tier that pisses me off cause its way too fast for how fat it is.
Giratina-A is a lot more refined, it has status (will-o-wisp), setup (calm mind), has WAY higher bulk in 150/120/120 compared to zama's 92/115/115, full coverage moves, and has a lot more roles especially being good on stall and offense while zama is mostly just offense.
I would argue Giratina-O is safer than Giratina-A cause;
1: can't hold an item. Sure orb makes its STABs hurt more but it ain't like other mons don't one shot the tier anyways.
2: lower bulk, giratina-O is 150/100/100, 40 BST worth of bulk missing which makes it seem WAY more killable, at least closer to zama's numbers. Reality is if you're switching anything into giratina, its going to get 2HKO'd by either form, so at least having a better chance to kill it sounds more reasonable.
3: levitate prevents it from pressure stalling all your PP, even if it was bulk enough. Granted idk how broken tera electric giratina becomes doing this but at least you can potentially out stall it.
4:
there was an april fools joke suspect in generation 6 that had giratina-O in it rather than giratina-A, what's funny is some of the post were clearly playing along the joke, but there were a few arguments not getting the joke and actually going in-depth at some point in the thread, leaning on it still being overwhelming but not as overwhelming as you'd first expect.
And I still wouldn't want to see that drop down.