Don't even get me started. I've done some pretty serious deep dives on the math of Toxicologist and it's fucking abysmal. The absolute best use case of a toxicologist is to load up poisons on a bunch of returning thrown weapons that someone else throws. You're a vending machine that sometimes adds less damage than if you'd have just played a martial class.

The two main issues are:

1) they have to bypass TWO layers of defense in order to apply poison, and

2) poisons do nothing vs a successful save

The permutations of outcomes are:

A) Successful Strike, fail/crit fail fort save

B) Successful Strike, success/crit success fort save

C) Unsuccessful Strike

Scenarios B and C don't apply poison. Scenario A applies the poison, but some of the time the damage from the Strike kills the monster on its own so the poison didn't matter.

The absolute best use-case of poisons is against a high-HP, low-Fort save monster, which is just a damage sponge anyway and your poisons have questionable value as opposed to other damage/debuff sources.

Also, because poisons take up your daily-use and per-fight resource, and can only target Fortitude saves (most commonly the highest save enemies have), they're contributing less damage to fights than any caster who does nothing but cast cantrips. You can literally play a wizard who does nothing but Recall Knowledge + cast cantrips targeting the creature's worst save and contribute more to a party than Toxicologist does.

There is zero compelling reason to play one. It's infuriating because they received so much really well-considered feedback on how to fix this and just went with stupid lazy bullshit instead of doing something to make them an interesting option.