Fall of the Thran + Evolution Sage + Retreat to Coralhelm + Xavier Sal, Infested Captain + Zuran Orb

How it works

At the beginning of your precombat main phase, Fall of the Thran triggers, putting a lore counter on it.
Fall of the Thran's second or third chapter ability triggers.
Holding priority, activate Zuran Orb by sacrificing a land, causing you to gain 2 life.
You may optionally repeat step 3 one additional time.
If Fall of the Thran has three loyalty counters on it, activate Xavier Sal's first ability by tapping it and removing a lore counter from Fall of the Thran, causing you to populate.
Resolve the Fall of the Thran chapter trigger from step 2, causing each player to return two land cards from your graveyard to the battlefield.
Whenever the land(s) enter the battlefield, Evolution Sage and Retreat to Coralhelm trigger for each land that entered the battlefield under your control.
Holding priority, if the land(s) enter the battlefield untapped, you may activate them by tapping them, adding at least .
Resolve the first Retreat to Coralhelm trigger, untapping Xavier Sal.
Resolve the second Retreat to Coralhelm trigger, if applicable, either causing you to scry 1 or to tap or untap target creature.
Resolve the first Evolution Sage trigger, putting a lore counter on Fall of the Thran.
Repeat from step 2.
If applicable, resolve all remaining Evolution Sage triggers, causing you to proliferate that many times.
If you sacrifice and return two lands each cycle, this combo will net infinite untap of creatures you control and infinite scry 1.

In which brackets is this combo allowed, per Spellbook's Ruthless tier?

1–2 · Exhibition & Core

Spellbook classifies this as Ruthless — not for these brackets.

3 · Upgraded

Spellbook classifies this as Ruthless — not for these brackets.

4–5 · Optimized & cEDH

All combos are allowed.