Defensive stats, DPS mage items, and the new Viktor build
Defensive Stats
Big thing I want to talk about right now is why Adaptive Helm is probably my favorite MR item in the game, and why Mask is probably the best. The reason being when you compare DPS vs. burst builds, you see champions like Ahri doing oh let's say 3k damage in a rotation vs. an ADC, and Vlad doing roughly 2k in the same combo. That would be fine if you didn't note how quickly he can set off these rotations, compared to what she can burst after dropping her kit. Burst mages will always have higher damage, but because of the way DPS mages have so many nice tools in their kit (Cass Q MS, W grounding, AoE stun) that help them deliver the damage, they can usually pump out a respectable amount of burst and then keep trading for obscene DPS values. This is why you see champions like Ryze, Taliyah, and Ori remain staple picks. It doesn't help they also tend to have absurd amounts of tankiness or other tools that overshadow their burst counterparts.
This is where Adaptive Helm comes in. It does have some MR and HP, which is far more detrimental to burst mages than DPS mages (if you've ever gotten all inned by Talon but you couldn't burst him because he had a Hexdrinker you know what I mean), but the item's passive makes it far more useful for mitigating constant damage from successive spam-casts. I think a lot of items should move toward this kind of system because it allows for resistance nerfs so the items don't perform as well against burst champions while still holding ground against DPS.
Instead, we have items right now like Abyssal Mask that offer so much in raw sustain that the strongest mids can take it and their DPS output is still respectable while making them impossible to burst. Look back at the last couple of pro games and you'll see Mask on Ryze, you'll see it in high level Cassio games, Azir, etc. It chokes out the mages that are trying to burst and snowball because these champions just easily become impossible to stop being defensive items > offensive items early on and these champions will abuse it to outdps you. I also fear with the upcoming Archangel's buff that the champions synonymous with the Tear Mask build (again, Ryze and Cassio) will become overbearing.
DPS mage items
I'm actually very happy with the choices Riot is making in regards to splitting up Liandry's passives (HP burn + flat pen). I think that this is very good for mages because the flat pen and grevious wounds (combined with the buffed damage from Luden's or GLP) makes it strong against squishy teams and Liandry's will be its own tank-busting item that won't completely shut down tanks because of how quickly you're itemizing mpen. This is a solid nerf to DPS builds and I'm hoping it makes them less strong picks so that their coordinated-gameplay powerlevel goes down, their solo queue winrates drop to unacceptable levels, and they buff them so that they're real picks outside of D3+ and LCS players.
To explain, there are some picks that are overpowered because they're overpowered, but meta isn't about being the best at any one thing. It's about being the most consistent option 51% of the time. By toning down the ubiquitous power of Morello Liandry Void builds Riot's forcing diversity in who you pick because of their interactions with items. Some champions can go multiple routes but this will make it so there are definitive routes in general. It's like runes reforged. It's not good because it'll give champions multiple routes. It's good because it gives more in-class variance (only class I see with consistent rune pages is AD and you still have Klepto Ezreal, Comet Jhin/MF, and PtA Lucian).
New Viktor build
I've played 3 games with new Viktor in D4-D3 elo and I can definitively say that it's ungodly strong. I never expected the FFW-precision build to work as well as it does but it's quite hilarious, if a bit oppressive. I'm happy with the buffs and I think people should definitely try it before thinking Viktor is still too weak.
Build is Fleet Footwork with Presence of Mind, Tenacity, Coup de Grace and Sorcery's Celerity and Gathering Storm. The full tank build is IBG Mask with Liandry's and Void. You can swap out Mask for Cap or IBG for Lich Bane however I'd recommend against getting Lich Bane as part of what makes the build strong is how much damage you get for building only 2 real AP items + your Hex Core.
That being said, I think a lot of it is based on how strong Abyssal Mask is. Adding % damage to a tank is strong, but adding a % damage multiplier only begs to use it on people who output a high amount of magic damage anyway. I don't imagine it'll stay too strong if that happens and once the AP item pass goes through.
tl;dr I like the work Riot is doing with AP and MR items currently, including the work done on buffing Adaptive Helm. I also think that when Riot adds a bruiser keystone they should work on changing armor items to behave more like Adaptive Helm because that will help burst champions far more than any other change Riot can make.
I also like the work being done to split specific mages' overall power and buff up other champions who have fallen behind because they can't use DPS mage items.
Lastly, I'm glad Viktor is good again but I'm hoping the item changes put him back in line because it would be sad to see him get nerfed back to his previous state over how good his itemization is.