I don't really care about tiers so much, but when it comes down to character strength, I'd say Kohaku/PCL/HisuKoha/Ryougi are pretty far from S-tier.
Remember what a tier is - a comparison of how a character performs in matchups against all other characters (assessing their strength in the game.) Like Nero in MBAA, P-CL has some really bad matchups. C/F Koha aren't what they used to be (especially after cactus nerf). The OTG Relaunch doesn't really benefit either of them too much. OKAY PFHOR SHUT UP I DON'T EAT SLEEP AND BREATHE HAGI/IEDA C-KOHA VIDS
Maybe a bit of a different story for Hisu-Koha/Ryougi. Same can be said for Hisu/Koha about cactus, but I don't think it effects them as badly, and Ryougi getting buffs is pretty crazy. Maybe they're up there, but I don't think any of them are straight up unfair. Like Kanna and Sat said, it's probably a A+/A/A- difference at best.
I'd say Seifuku and Satsuki are floating up there around Hisu-Koha and Ryougi, personally. Satsuki's normals are much better now, and Seifuku's carry you to corner from anywhere and do 5k feels bad man.