Byleth weighs a little bit more than he should, at least with Angeal affected by whatever it is in this world which means he can't quite punch through boulders anymore... but he's still a pretty big guy who was in the military. He can manage this much.

He would make himself manage this much, no matter what.

"Is that so surprising?" Angeal asks him quietly as he begins to walk, holding Byleth as close as he wants. "All that information in your head, in this kind of place... You're going to need a good sleep, and a better breakfast, before you can even begin to figure all of that out. I can tell. So just focus on things step by step. And I'll be there with you. To help you out. Alright?"