That’s not a skill bonus, the skill bonus is a few rows above. Afaik OP is actually correct that this is a leftover from previous behavior since I recall reading that the cap of the burst summon is 20 now.
you’re right, and it seem to affect more on-crit devotions (like reckless tempest, assassin’s mark and living shadow) and more damage dealing debuffs (like word of pain and haunt) as well. phoenix fire on the other hand works with necrosis.
i don’t think you got it wrong. the way it’s worded at least. it added +1 to the number that was summoned each time and the other modifier would have added +1 to the max summon limit. the increased skill level is further up the list. as it stood that would have increased a base summon limit to 4 and summoned 2 at a time, i believe
test patch added 20s cooldown and increased burst summon. the patch notes state we summon “all at once” which one can read to imply to dynamically scale with increased summon limit making +1 summon mods unnecessary. the implementation is different so that’s where the confusion comes from.