As a veteran player, who has A LOT of knowledge and time spend into the game, bestiary league is by far the worst thing that has happened. Even talisman league was somewhat enjoyable compared to this. The mechanic is so clunky, the vast amount of dumb knowledge you are required to learn is straight out stupid, compared to the overall complexity of the game, which further pushes new players to strive to learn the game, instead of copying some popular build. Now getting in on how to improve the league:
Recipes should no longer require a mod on a beast. Its insanely hard to check every mod on a dog, its name, its rarity and consider the lvl on the map makes this dumb. No more searching for flying, bombing kangaroos that spit acid spiders and die in fire explosions. Note I said "searching", not removing this. They are fun.
All beast should have a rarity. From normal/magic/rare/legendary to ancient. Each specific family of legendary/ancient beasts provide the highest or most valuable recipes OF THAT FAMILY. All others are fluff to the rcp.
For example an ancient wolf gets you access to the rcps that the feric crapy red 80+ alpha shit let you do. That way, the moment you encounter a legendary/ancient beast you know, shit is up, and u gotta kill it and it means business. Preferably they can be purple or black on the map. This way I WILL NOT SKIP OVER A FUCKING DOG ON THE MAP.
For portals you craft 4 different beasts that randomly spawn, they have a unique status and are color brown-ish.
For more difficult recipes you change the requirements from 2 to 4 legendary/ancient + rare beasts or different types. This will be the basis of where you can tweak and adjust spawn rates.
Make it so I can release the beasts from the zoo by either fighting them or just releasing them when its full.
Display a message EVERY TIME YOU CAPTURE A BEAST and the cell for that type is full, or at least use an icon on the beast name to indicate that your zoo is full.
If you create an environment for a new player to LEARN the game, they will hang on to it for far longer than they are now. This 1 month spikes in playerbase shows how players are reacting to the current state of the game. Of course, you can get the really poe orbs cheap here, U4GM is a reliable online PoE Service store, where players can get all kinds of items and currency that they wish to obtain in Path of Exile!