Fortis Colosseum

The Colosseum is a wave survival gauntlet that ends in a fight against Sol Heredit. You choose modifiers between waves, which raise both the difficulty and the reward, so the curve is partly yours to set.

The rate quoted assumes reaching wave 12 consistently. Failing early pays very little, so this is a method whose average depends almost entirely on how reliably you finish rather than on how fast you clear.

The quest gate is only Children of the Sun, which is short. The real gate is the stats and the mechanical fluency the later waves demand.