I love the current system, since it means Gozer got a buff to proper companion level rather than barely a footnote to Dackly,
There are three factors at work here, and I think this is crucial
Summons able to be put on the field
Summons Available To the user
Summon's Power Level
If you ask me, it should work like how I am planning, Summon power is based on how many can be out at once.
If you are only able to have one summon out, it should be companion level.
Each additional one cuts everything they have by that amount, period, anything else is highly OP.
This should be a hard lock, so you can't pick and choose how many summons you can make in battle to reorganize their power level.
so if you can make 10 minions total, each one will be 1/10 companion level, have 1/10 AP, 1/10 SP, and 1/10 Level.
Minion clusters should be a thing if you want multiple, so you summon a hoard of rats as your summon? That is one companion level summon, and works accordingly.
With no pussyfooting around the issue and trying to make it pretty, if you have 2 summons, it is only fair that they each be half as strong as one bigger summon.
Second, once a summon is summoned, it stays until dead or battle concludes, outside of very specific circumstances, so if you have 5 companion level summons, you cannot swap them in battle, but you can do so before battle, or after they die, you can summon a different one.
Third, Each summon needs it's own skill, and a perk for summoning related to the general summon concept.
If summons are merely variants, or all run off the same number sceme, then you can simply add a level to the skill to increase the amount of types.