TLDR: yes they've slightly fallen off, no they're not "replaced"
Shadow Dialga, Shadow Garchomp and Kyurem Black appear to be better than Dialga-O in no-Party context. Normalizing dragon type "power" as Haxorus at 100%, we have Rayquaza (DT BS) at 104%, Dialga-O at 110.3% and Shadow Dialga at 112.3%. Please note this new Regidrago (DB-DE) slightly overpowers Rayquaza. Of course Mega Ray would be in a tier of its own here, at 144.5%.
With Party Power, it's a little different. Dialga-O remains the #1 Dragon, but Shadow Dialga is immediately behind. Considering the standard Dragonite (DBreath-DMeteor) as 100% Dragon-type power, we have Dialga-O at 129.8% and Shadow Dialga at 129.1%, then Palkia-O at 121% and Shadow Palkia at 117%. Mega Ray isn't even the best pokemon here, falling behind both Dialgas at 123%.
in conclusion, yes they have slightly fallen off, but they're still top tier Dragon types. Dialga-O is an S-tier pokemon, Palkia-O is A+
sources: DialgaDex
Yeah, never intended to say that they're "bad", simply that they aren't the ABSOLUTE TOP of the type that they were at their release (minus Mega Rayquaze) any longer. They're still OBJECTIVELY GREAT.

Hey hey, don't know where to post this, and sorry to be "that guy," but I noticed that under Tinkaton's listing it still states she has access to Brutal Swing- I heard that the move was taken away shortly before her release. You've taken it off the Moves list, it just references spamming it later in her pVp moves description. Threw me off is all 😏
> … the Origin Formes have strong utility, though they’ve fallen off recently
Why have they stopped being so useful? What has changed? What has replaced them? I’m in particular interested in finding out what replaces Dialga O
Anything weak to steel is going to wish it hadn’t been
Will you be putting out a Crowned Zacian analysis soon? Given the ATK stat + its typing I am really looking forward to your thoughts :)