While it may sound good in theory, a trade system would be open to massive abuse. Early in the game it is quite easy to get some quick sacred shards, and anyone could create multiple accounts, open the shards to get random legendaries, and then trade them onto a single account
Very much this
I've finally got three trained, after eating a few dups without realizing the value. Wish I hadn't eaten that dup Husk.
edit to be fair I ate him before hydra was introduced.
Can't really blame you.
Husk's value went from kinda meh to "yeah i'd take 4 of him" with Hydra/Hard Spider.