Now that we have got the stats and movepools of all newcomers, I will finally complete here my segment about the upcoming Pokemon. Also, my expectations about the Tapus are now gone due to not receiving their terrain-boosted moves. Anyways, with the exception of the two Calyrex forms who are as of now in Ubers, I will write about all the new OU-legal Pokemon.
Galarian Slowking: My wish that it should keep Regenerator was granted, and now that it has more offensive presence than regular Slowking, it could have a potential niche in OU as an anti-stall Pokemon with its signature move draining PP. Now with stall expected to rise due to the broken 'mons such as Blaziken and Pheromosa currently residing for now in OU, it would be a good chance for Galarian Slowking to have a valid niche.
Galarian Articuno: Unlike regular Articuno, it has larger offensive presence thanks to an improved 125 Sp. Attack, however it has the same flaw with its Kantonian counterpart, which is lack of coverage. Also, it has a very serious flaw in not having any recovery whatsoever. I don't know where it will end, most likely in UU or RU, but slightly behind its counterpart due to longevity issues.
Galarian Zapdos: Galarian Zapdos has the largest potential out of the three Galarian Birds, due to its offensive typing and strong coverage in Close Combat, Brave Bird and Blaze Kick. In general, we saw from Hawlucha how good Fighting/Flying is as an offensive typing. If it had Roost, it would have been even better, but it has potential as a strong physical attacker and could see the light of OU.
Galarian Moltres: Unfortunately, Galarian Moltres is screwed in many factors, such as not having the same offensive power as its regular and quite hyped counterpart and of course, no recovery which means it will be outclassed by Mandibuzz on the defensive part. Offensively, it has a decent movepool and even Nasty Plot, but I believe that the stat change from regular Moltres leaves something to be desired.
Regieleki: Arguably the best Regi ever made, and as of now the fastest unboosted Pokemon in history. I mean, 200 Speed is out of this world. However, it has a horribly shallow movepool that leaves it neutered by Ground-types and mandating teammates that can deal with them, but under the right circumstances, it can fulfil its enormous potential by Speed alone and find a proper niche as a late-game cleaner in OU.
Regidrago: Sadly, Regidrago is just an epic disappointment. It has 200 base HP, but it can't utilise them properly due to its weak defenses. Also, it is obviously Fairy-type fodder due to its typing and said defensive problems, but luckily its movepool is bigger than Regieleki's. It is essentially Guzzlord 2.0 as stated by other users and will pretty much reside in the lower tiers.
Calyrex: What can I say? I knew from the beginning this Pokemon would be a worse Celebi, but did not expect this to have such a poor stat distribution and shallow movepool. Luckily, its two fused forms can do something well in Ubers, but regular Calyrex will go straight down to the low tiers, most likely NU at best and PU at worst. One of the most underwhelming legendary Pokemon we have ever seen.
Glastrier: A victim of Game Freak's idea about most Ice-types that will not allow it to fulfil its enormous offensive potential. While it hits hard and has some good moves to use, including Close Combat for strong coverage, base 30 speed is awful even by Ice-type standards. Hopefully Trick Room will allow it to have a niche, but I don't see it in OU, most possibly UU due to its awful speed.
Spectrier: Spectrier is pretty much a stronger Gengar but with worse movepool. I don't know why those new legenrdary Pokemon have shallow movepools. The good thing about Spectrier is that with the proper team support and good teammates that can handle Dark-types, is that it can become a good sweeper, especially with Nasty Plot being one of its few good moves. I think it can stay in OU as a decent sweeper.
And that is all I have to say about the new OU-legal Pokemon released, which means my 3-part segment is officialy completed.