In theory a light metro would allow more flexibility for the route to veer off to serve important destinations and provide better connections, whilst saving on operations and maintenance costs in the long term. For instance, you could have the light metro divert from the corridor to have a direct interchange at Sheppard-McCowan and a better connections to Line 2/4, rather than forcing everyone to walk 400-500m like at Main Street-Danforth. Building such infrastructure with BiLevels in mind would significantly increase the capital costs for any such diversions.