Simply put the 50lv arc is not bad because of the grind itself. But because of how annoying is to even kill one of them.
Main issue is penguins atleast to me.
1st, their map is too small, its a small cave entrance that feels too small for what should be a mission such as killing them, or collecting 80 of their items.
2nd, i feel additional bigger room, or ingeneral big room for them is needed, due to how much aoe or dmg they do. Similar to how cursed host mobs have giant room, are around their level, but you have space to attack, this map they are placed currently doesn't feel right to me.
And i know someone gonna say "Just grind the penguins at the snow leopard" And to that i say...its..too little? There is 2 penguins on that map for a bit of -safety-
I know this arc is end game content atm, and i know is supposed to be difficult and challenging the player, but this difficult spike is not done due to the mechanics of the mob itself, but rather how tiny, and almost unable to do anything feeling like.
My only suggestion like ive said earlier at this post is either expand the cave map for them, or add a new room thats big larger at size so someone can run and do the missions related to the penguins much easier.