The Batman is actually the worse argument for the redemption thing, all of that just because of the Joker, he made so much damage to million of persons at the point the fans thinks Batman should kill Joker, even in the same comics Harley Quinn tells Batman he should kill Joker.
The Joker is the representation about not putting limits to the redemption and i know that applies with Discord but that’s the thing, if Discord can’t be redeemed at all by mane6, why would the equestrians want to redeem Tirek, Chrysalis and Cozy which made a racial war, and Chrysalis done worse things previously without be jailed?
The problem isn’t about if they forgot the trio or not, the trouble is the nepotism which was the result of the Grogar’s twist and status quo, if Grogar was the final villain and redeem the trio with their actions everything will be fine, if they stoned Discord with the trio everything will be finein moral but people will discuss about how awful was the script.