You honestly don't need to be an offensive character to make good use of Toxicologist. Just look at Wriggle. And you don't need that much ATK/MAG to be able to make good use of the heals on Renko. It still heals for a good amount despite her low magic (If you saw my picture I get 10k MAG with 3x Grand Master Titles) I did some heals and it's good enough to heal for a good amount. There's also the fact that Renko is very fast with maintenance, so healer being bad on her wouldn't make sense. Healer is good on Aya because she's so fast, and Renko goes super fast too. That speed also helps with Toxicologist, you can move fast and do your thing.
Imo, Enchanter is still the best class for her though.
That's why I said "by that logic", ZXNova. If being fast helps in terms of being a Healer, then you may have a solid point there. Also, I'll presume that either your main equip boosted your magic to the way that it is or that you spent some levels in her MAG stat to do so, because her ATK and MAG growth are equal last time I checked.
Wriggle only really uses toxicologist because her poison infliction is her actual damage and there's not really anything else going for her but Team 9. Her spell that gets stronger with inflicted Poison would only be worth a use with a big team 9 boost, so for the most part, inflicting poison is the only job she has, and outside of Team 9 uses again there's not much reason to set her up for doing much else than being decently bulky. If you aren't having Team 9 active a lot than she isn't bulky enough to really be more than an offtank either, so setting her up for support is meh, even if she's got Poison Touch to synergize.
Wriggle's probably the only person I'd consider putting toxicologist on outside of just expanding Marisa's elemental options with a side of Sheer Force synergy. I never tested how strong the spells are but it'd probably be half-okay at least. It seems like a pretty meh subclass to me. Maybe someone who self-inflicts ailments would like Toxic Conversion? It's counterpart hexer has more relevance since it's much more worth using in tandem with Sheer Force (even if your choices of 'tanky' are Kogasa, Utsuho, and MND-Marisa; Kogasa has some tank synergy and pretty nice def though) and for Hina. Maybe it'd be worthwhile for Reisen to get a lil' boost but she's already got a lot of nice things to expand upon in other areas.
Well, I can easily see who can make good use of it, if it's okay for me to say it...
1. Yuuka. A sturdy mage with Extra Attack means that the potential to cause a heavy, if somewhat unreliable, dose of ailment inflicting is present, while Encounter with a Formidable Foe allows her to power up well while doing so, depending on the damage formula on said spells. On top of that, she has her "Beauty of Nature" spell card to make said ailments last longer on foes once they do stick, so being able to inflict them herself makes it all the more useful.
Speaking of people with Extra Attack...
2. Orin. As a fast composite attacker who can make good use of Extra Attack herself, Orin can use said spells for the same reason: possible heavy dose of status affliction. However, she can also use the boost for her Cat's Walk, as inflicting Shock can be useful in the right situation. I think that I remember that she has another spell that inflicts status ailments, but I can't seem to remember which one it was. However, being fast will also allow her to not mind the 50% post time gauge much, while being a composite user means that she can at least have a better chance of dealing damage with said spells than other speedsters sans Marisa and Renko(although I would note that the main purpose with these spells for Orin is to deal status ailments, not deal damage) while having better defenses than the former and having her far sooner than the latter.
3. Yuyuko. A mage with the highest Death inflicting spells in the entire game, boosting said power can only be useful to her. The first three spells of the subclass can also increase her elemental coverage past SPI and DRK as well, and unless I'm mistaken, the subclass's learnable skill for resisting all status ailments does stack with Hakugyokurou's Mistress for resisting Instant Death, which helps in the right situation.
4. Alice. The reason for her to take this class is mainly for boosting the strength of her Tripwire spell, which is already strong on it's own(unless someone can tell me otherwise, I'll presume that the boost to inflicting status ailments from the Toxicologist is like the boost to increasing buffs from Enchanter: the stronger the effect is to begin with, the more potent the percentage based boost becomes), leading to more chances to use Final Blow to help in her dealing damage. Also, unless I'm mistaken, Alice has Fire, Mystic, and Physical elemental attacks on her own, so adding the subclass's spells gives her access to seven out of eight elements in the game(Seven Colored Puppeteer, indeed), so there's that.
5. Reisen, as you yourself had said. Her Intense Vertigo already makes it easier to deal status ailment for the spells that she has, and she has People of the Moon to remove half of the defenses that would prevent you from dealing damage in the first place. Like Alice, she has Final Blow(unless I'm mistaken) to increase how much damage she can do, and the subclass's spells being added to her own gives her the ability to inflict every status ailment in the game, which works out very well for her due to her skills and the subclass's skills having a whole lot of synergy together. Granted, she can also use Hexer to power up the effect of her debuffing attack spells(Discarder comes to mind) and I would not be surprised if many people simply went with that, but Toxicologist powers up the effect of some of her spells too, so it's far from a bad choice.
6. Satori. As she can use any spell that anyone else on the frontline can use, Satori can use the boost from this subclass for the various spells that she can gain access to. The spells from the subclass act also act as a back up set of spells that she can have regardless of the lineup, all of which cost the same as her silence inflicting MYS spell(which can also benefit from said boost). On a side note, it already has been said that MAG based Satori can use cards from Suika and Komachi to melt faces, and the spell gained from the latter(Narrow Confines of Avici) benefits from the ailment inflicting boost, since the original user would use the same spell for exactly that or debuffs(which Hexer helps in).
I will state that I may be overestimating the boost from Toxicologist and the value of the elemental coverage that it gives(it's the only subclass that gives a CLD element spell) by a lot, but then, that's why I bring up stuff like this with you guys in the first place. Discussion and all that.
I hope that I wasn't being rude in anything that I was saying...
