@Vlad, solid points as well... I really like the idea that more powerful entities, especially intelligent ones, require bartering for their services. I just don't know how well that fits into the models above without some additional mechanics (which I'm trying to avoid).
RMSS seems to have tried to combine Summoning magic with a set skill: Summoning, meaning that you needed to invest DP into being able to summon the appropriate entities. It's certainly a way to go, although I'm trying to avoid yet another DP sink for characters.
Summoning is a very specialized class. A Summoner could probably snap his fingers and conjure rabbits and doves all day but unless you are serving stew and squab, the practicality is limited. A cast fireball is a tactical weapon that might harm a squad, while summoning a demon or dragon is producing a
strategic weapon that could crush an army. Do you really want a spellcaster snapping his fingers and popping in a demon or dragon every round? A nuke should cost more than a grenade and be far more complicated to make.
Isekai storylines work for the Japanese because culturally, the Japanese tend to obey authority so summoned people (including whole classrooms of children) tend to follow orders. There are few exceptions, such as in
The Rise of the Shield Hero where summoned heroes were killed for refusing to comply. In another series,
Arifureta: From Commonplace to World's Strongest, a high school classroom, including the teacher are summoned to be heroes and undergo training as fighters and magic users to fight demons. The hero is attacked by a jealous classmate during a battle and the hero wakes up many levels deeper in the dungeon. He survives, even though he's a weak support mage, he increases his power and clears the dungeon. He then decides to strike off on his own and the church that summoned him declares him a heretic for slipping their leash.
Summoning is more in the realm of ritual magic, which requires meticulous pre-casting planning and protections, especially when attempting to summon powerful, potentially hostile beings. I don't see how summoning gives the caster automatic control or even influence. At best, I'd allow a random reaction table prior to negotiations. I realize you are trying to make this simple but gating in an intelligent being that may even be more intelligent than a human should not be simple. Summoning a dragon would be like encountering one in the wild, but with protections up just in case you have to send it back. Such a summon should neither be cheap nor easy or it would be commonplace.
Last example from
Anime...
She Professed Herself Pupil of the Wise Man. This series is about a Summoner...but he's the most powerful wizard in he world, so he does snap his fingers and drops strategic level demons on the battlefield... This is a bizarre MMO-based series where a veteran player who took a few years off from playing restarts his old, legendary character and while redesigning his avatar, falls asleep at the keyboard and wakes up as a teenaged girl...with godlike powers, able to summon Valkyries and giant, demonic knights. The character is so high in level that it can melee with demons and beat them, so not a very good measure of your average Summoner, but how many specialists in summoning are there? The complication is that the character is unable to log off from the MMO so it is sort of an
Isekai theme.