I suppose this is one way to look at it.
The ESR has about 50% spare capacity, train loading, as running mostly 20t/h anyway. Open to correction.
So about ~10,000 per hour spare on ESR.
The LR is rated at what 15,0000 per hour. Open to correction.
So if there is a claim the LR will be maxed out then the ESR would have certainly been maxed out. However the ESR would have have also had significant counter flow ridership as well.
Having stated that to me this would have still be smarter over LR and likely lower cost long-term as extra operating cost to rail would have been bigger all. May have also been positive cash flow.
The excess capacity could have easily been left on bus, so like now but less bus density on roads.
The western Meto cannot cannot to Nth side as no capacity remaining after Bankstown. So potentially if capacity was an issue for ESR the western Metro could have been extended to have stations at More Park and NSW University next to ESR, that's if required and would be built late 2020's.
The city CBD LR could have still gone ahead buy with the line heading south to Woolomoloo and Green Square area and also allowed the inner west light rail to access the CBD Loop.