Large numbers of infantry as cargo is inadvisable, yes. But we're not talking about infantry. We're talking about 4-5 people per mech. That's 1 ton per mech per day. And since an Ares weighs 135 tons, that 220-ton bay can theoretically house the mech and crew for 12 weeks. Since 4-5 weeks is a much more reasonable load(one week out, one week in, a few extra weeks for recharge time and shit happening), that's a total of 171 tons for the mech, the crew and techs, and five weeks of food/water. That leaves 49 tons for pods and other spare parts. And that's in their dedicated cargo bays. The Duat still has almost 700 tons of space in the main cargo bay, more than enough for the smash raids it's described as being used for. And if you're running one in a more standard deployment, then the fleet carrying the rest of your troops is already expected to have a complement of supply ships like Mules or Mammoths.