In Path of Exile, I hate Bestiary, but its sudden disappearance gave me some disappointment. I have to say that unlike poe currency buy, Bestiary does have a lot of flaws:
1. It doesn’t add mob density.
In a vacuum, this isn’t necessarily bad, but high mob density is fun and Bestiary not adding large amounts of extra mobs make it feel worse compared to other leagues. Besides being much more fun to fight large crowds of monsters, the lack of density in Bestiary had pretty large effects on currency and the economy throughout the league.
People struggled to sustain alcs for their maps and they struggled to break into red maps. It really highlighted the issues the game has with having a strong build but not being able to play content that challenges said build due to RNG.
2. The progression is heavily RNG-gated.
Finding the specific beasts you need (without trading for them) can be incredibly tedious and painful – there’s no way to target farm for specific rare and legendary beasts, and specific mods don’t occur often enough that you’ll be finding them regularly.
This makes reaching the league’s end-game – the spirit beasts – feel entirely beholden to RNG. Abyss has a similar issue with its Depths spawns (but it doesn’t feel as bad because it has all the added monsters).
Look at leagues like Breach, Perandus and Harbinger, where you get a small amount of progression for each and every time you interact with the league mechanic, via breach splinters, coins or shards. With Bestiary (and Abyss) you can interact with the league mechanic many times in a row and not progress at all, which just feels bad;
3. It doesn’t really have its own, immediately identifiable aesthetic.
This really shows during the current Flashback race – it’s very easy to identify Breach monsters, Harbinger monsters, Abyss monsters, Perandus monsters, along with Breaches, Harbingers, Abysses and Perandus chests, all with a quick glance.
You know exactly what kind of mechanic you’re up against, what kind of reward to expect, etc. With Bestiary, the monsters often just look like regular monsters, especially if it’s particularly chaotic on-screen. I’ve had situations where I’ve not even realised I’ve been fighting a Bestiary monster. Sure, they’re marked on the map, but I don’t think that’s enough.
Personally, despite the list of negatives I’ve just given, I’m disappointed Bestiary isn’t going core. While I don’t think it was good as a league, I think it’d be a good addition to the game.