I just looked at the Deuter carrier on line and it looked substanial but I haven't seen on in person or worn one.
We liked the Kelty although it could have been 3-4 pounds lighter if the fabric was thinner and less heavily padded. It's designed for day hikes and around town more than for thru-hikes.
Some things to look for: You want some storage for around town use - diapers, snacks, change of clothes, etc. When used for backpacking, you (dad) usually carry all the gear while mom carries the kid and kid stuff, IME. But volume is an issue. A carrier that lets mom lash on a sleeping bag helps with the volume problem while not shifting much weight to her.
A number of our trips were with our 2-year-old in the carrier and another "bun in the oven", so she was hiking for 3, while I was packing for 3/4.
Some carriers have sun shades that afix to flexible rods inserted into the carrier. Those are very helpful.
The carrier HAS to stand on its own when set on the ground. You/she need to be able to get things from the pockets, go pee, etc, without having to hold the baby in one arm. Check for how stable that position is while in the store.
This sounds goofy, but do it: Get a little mirror and fasten it on a wristband. Then mom can check if the baby is out of the sun or has spit-up dripping down her back, etc. It is a LOT easier than taking the pack off and potentially waking the baby.