First of all, poison provides dwarves and halflings with an obstacle when it comes to thieves/ninjas. Therefore, this would be a workaround that they don't need. Additionally, at least poison gives the opportunity for thieves and ninjas to play it safe, as there is a visible thing affecting you every round, so they know when they can/cannot attempt a blackjack.
Size also allows individuals to wield two-handed weapons with a shield (may or may not be a bug), which would allow ridiculous offensive output coupled with ridiculous defense. For example, wielding an arctron with a shield? Ouchy. And you can say that there are other sources of enlarge that allow the same thing, but none so readily available as a spell in your repertoire.
And I am fully aware we're not talking about the enlarge spell. I'm just saying, there are some perks that I would rather not see go to a divine intervention that is already arguably one of the best divine interventions.