Vadim, Murmur, and should be A IMO - the rest of the Bs are a clear step down from them
Vadim has utility with mug, steal heart, steal time, etc - good thief stuff with high evade and resistances. A bit on the weak side in damage but has 2 attack up passives too
Murmur has very good damage resistance for a tank, much less a mage. But a tiny HP pool. She takes some investment in good armor, espers, and cards, but she can shrug off the damage better than many UR characters while having a strong attack in Jammer Thrust
I also suggest grouping SR, Rs and N together, given there's not any real difference between them.
The tier system itself also needs soem work done to it.
It's obvious Phoebe is the standout SR unit, being comparable in terms of support to similar role MRs (Helena, Fina, Margritte).
But it doesn't mean all others are at the same tier.
Vadim, Mia and Zazan are in their own tier due to access to steal time and steal heart for instance.
Other than the thieves, the ones with access to supporting kits (white magic especially) also deserve special mention.
Vallaide has the highest TP pool in the game and access to green + white mage combo, with moderate MAG and AGI stats. That means he can use a ton of support skills (Imperil, cure, cura, curada, full life, protect, shell) non stop.
Nayah has the 4th highest Mag stat in the game now with full access to white mage kit and double healing skill set with white mage + cleric combo, making her healing support incredibly reliable (high number of uses + healing output) for tower content.
Murmur might not be a powerhouse like higher tier mages, but she's got access to Flare (element neutral spell with high modifier) to deal with high DEF/low SPR enemies.Also, her unusually high mitigation stats (tank tier) make up for her low HP by quite some degree.
Due to resource scarcity and future content promoting comp diversity, I feel it's important to clearly assess SR/R/N's viability properly.
I'm just a casual JP player, but we often see guides about Tower floors mentioning the need for more units, especially the cheap to build ones like SRs.
I agree it's a good idea to rank SRs, Rs and N together and give the tier list more depth.
Phoebe and Murmur should be S tier list for SR. High Dmg Mitigation, Phoebe best support, Murmur can be semi-support dps
Idk man, murmur seems pretty OK especially considering sr's are way easier to get maxed than mr/ur. She ends with like 30-60% resistance to every single attack type plus an extra 10% to all element resist. A decent hp Stat (about same as yshtola) and knows offensive spell and cura by default. I'm thinkin she could be worth maxing given the much lower cost to do so.
Unfortunately, SRs in this game have very low stats compared to MR and UR units. I recommend you to use MRs like Khury, Fina, and Rairyuu. at least for now. Even if you are a F2P, you can make MR units grow smoothly.
I would prefer if we had a tier list subsection for each individual Rarity as well as an overall tier list, I know some games some of the lower Rarity units can still do some work or can be just as strong as some of the higher units if maxed out, such as dragalia lost.