Whether potion poisoning is benificial or not is up to personal preference and context. When I'm farming bitw or anything that is adv or lower for example I don't care for losing all my crit from my will (although I wouldn't drink HP pots in bitw that much so that wouldn't really happen), since I either don't use skills that need more than 30% crit, or their prot is low anyway. In elites and some hardmode dungeons I don't really embrace potion poisoning, since those don't consist of 100% spin to win and I'd like to keep my crit.
Also, no archer would want to get potion poisoned at almost any time. Or water alchemists. And mages... don't care about str loss from mp pots, but they can't use hp pots while poisoned due to int loss so unless they don't use hp pots ever, they don't like it either.
Increasing the stack size of smaller potion denominations literally disincentivizes using larger ones by design because Mabinogi lets you pop potions as fast as your finger can mash the hotkey.
Rather, as fast as ping allows you. With an hp pool that can reach close to 400 when high lvl and stamina pool of 500, it can take quite a while with 130-150 ping to get it all back with 30 pots.