He is postulating they did not have material, the implacation from 3145 is they do not have bodies.
First up, he's also one of the writers who helped the very material we're discussing.
Second, check TRO3085. Post-Jihad, the Exiles were suffering chronic shortages of Clan-tech equipment. That's why they created the IS Tech
Mangonel and mixed-tech
Pack Hunters, and also part of why they were unable to restore their lost
Mad Cat, Puma and
Fenris production. That would also limit their ability to rebuild their forces, especially in light of the losses they suffered during the Jihad. They could have raised new Sibkos, yes, but those warriors wouldn't have had 'Mechs to pilot.
And that's before we look at events that occurred between 3085 and 3132, which are still not fully documented. They could have suffered other losses durign that time that they would have been unable to make up. For example, in 3099, the Exiles lost an entire cluster that were claimed by the Wolves. For all we know, they could have lost more.
Trading away a Warship that they had limited use for at the time for new material to help rebuild their forces and possibly even fix gaps in their production capabilities is a good deal.
The personell crunch doesn't occur until the 3140s, well after the point that they were suffering material shortages.