Imo the scaling should be this, in part one:
low tiers: Ryuga, Shin, Rei, Amiba, Jugai, Colonel, unmotivated Juza etc. "At least Low 6-B" because Shin one shot Ken who was already far stronger than Jagi, Juza and Ryuga are all relative to Shin either directly or indirectly.
mid tiers: Shu, motivated Juuza, Souther "High 6-A" because Shu while not fighting with killing intent can damage Kenshiro and hurt him with his attacks, Souther defeated Kenshiro, Juuza's palm strike could have one shot base Raoh if Raoh didn't divert the blow by hitting his pressure points.
End of part 1 to early Asura arc:
Upper mid tiers: Toki, Solia, Falco, nameless Asura, Alf "At least High 6-A" (they scale to Tenryu Kokyu Ho Raoh either directly or indirectly)
High tiers: Kaiser, Shachi "At least 5-C likely Low 5-B" (Kaiser is only ranked below the 3 demon kings, elite shuras can match a thousand shuras who are all relative or above the nameless shuras)
top tiers: Han, Jukei, Yasha, Hyoh "Low 5-B" (Injured base Hyoh and Yasha were folding hundreds of the elite shuras, Han smacked Shachi and Kaiser in the past, Jukei reacts to and blocks attacks from an healthy base Hyoh who says he is not going to hold back against his master in their "death match".)
God tiers: Kenshiro and Kaioh "At least Low 5-B" (30 % Kenshiro literally beats a full power, matouki amped Hyoh and Kaioh is stated to grow stronger in the final fight and he is at least as strong as Hyoh)