Summoning Skill and conversion: How does it work exactely?

[Alhanelem]

100% sure about this?

I'm pretty sure about this. Why would you have any reason to think otherwise? There would be zero reason to have any summoning magic skill + if you weren't at the level cap if it weren't the case. If you're level 60 and your skill is capped for level 60 and you have + skill, you should be getting increased buff durations. Testable in ballista- if you get the benefit below level 75, then

Do you put an item with +19 SMN skill or one with +10 Macc in a certain BP set?

Skill

A SMN Skill +8 or a Pet Macc+7?

Skill

I've never had an issue with magic accuracy. It seems to be naturally better than physical accuracy, as I haven't been having appropriate-element magic BPs resisting more than physical BPs miss. I try to avoid having to carry around more gear than really necessary when the benefit is likely imperceptible. (Though, the mog wardrobe may change this for me)

Keep in mind, short of doing thousands of samples with both +acc and no +acc, it's difficult to conclusively say here, because /checkparam can't tell you if an effect that only applies during a BP is applied. (and I just realized, that checkparam doesn't show magic accuracy anyway)

And if it does, does it work for BP: Ward debuffs or just for BP: Rage?

If it does, it would affect anything that targets an enemy. (Note that damaging pacts under BP Ward (e.g. diabolos) are still affected by the accuracy and skill as far as I can tell).

Duration of debuffs is testable in ballista, as well. I'd be lying if I said I tested that, but I have not ever heard of anyone reporting increased debuff durations from BP wards.