I noticed that there’s no indication of a Thrall’s Tier other than in their name. So, if you’re like me, and rename them from [Ethnicity] [Profession] [Tier] to [Reasonably Name]. You end up losing any ingame reference to their Tier. - At least that I can find with in the Vanilla UI (no mods; I play on Official).
I propose that the Tier be listed under the Level in the Info UI (Thrall radial dial, " i " button).
The convention should be Roman Numeral, including for Named; “Tier IV”. This future-proofs it if they add additional Tiers like “Champion” (Tier V) or “Hero” (Tier VI).
Additionally the Followers pane (list of all Followers) should also have a “Tier” column added. - I would suggest between the Class and Status column.