RC lifting the crate is a joke-less scene, so you can't dismiss physics there (IMO).
Sure, but in D&D, you can usually divide things into two distinct groups: the ones that are real-world medieval (or strongly inspired), and the ones that are fantasy/magic.I feel that assuming there is some kind of magic involved with presumably experienced hunters capturing a high level monster makes sense, and that they would have the resources to own a more expensive, potentially lightweight yet sturdy cage than novice hunters would makes sense as well.
In other words, I expect to see both "magical" cages and "classical" cages in the world. So, IMO, the hunters could very well have been equipped with a high-tech (a.k.a. magic) permanent cage like the moderately escapable one Xykon cast over Miko, bought from some wizard, but they weren't -- instead, they had what appeared to be a standard wood crate.
Sure, they could technically have bothered to get spells cast on that crate to make it permanently lighter or stronger, but I would personally see that as a weird, half-assed middle ground between good old sturdy standard crate and kickass magical crate.