I don't think limited wish is in the same tier as wish. It's a very useful spell, but not nearly as game-breaking.
Top-tier spells are usually the open-ended ones, the ones that grant additional actions, and the ones that bypass checks entirely. That includes the likes of alter self, polymorph, draconic polymorph, polymorph any object, shapechange, planar binding, greater planar binding, gate, wish, miracle, magic jar, ice assassin, simulacrum, animate dead, dominate monster, astral projection, Mordenkainen's disjunction, body outside body, time stop, and mind blank.
Some spells aren't necessarily very powerful in a caster-versus-caster comparison, but they change the playing field relative to non-casters, like teleport, greater teleport, plane shift, control winds, greater invisibility, scrying, even Leomund's tiny hut (20' radius sphere of force, 2h/level duration, 3rd-level spell, yes please!).
Fusion + astral seed is t0 (TO).
I don't think it's useful to tier all spells of a given level. Better to pile all spells together and tier the lot. Yes, there won't be a lot of t1 cantrips, but that's okay. We know caster power is based on spell access.