Agreed, I was just thinking that as I read about Dynamis accidentally killing Astalos. A Power Level 12 spell with the ability to instantly kill someone? That's much too easy.
Perhaps you could spread out power levels a bit, so instead of 1-5 we have 1-10 and have more subtle changes between the levels? Then keep everything else the same. So progression will be slower, but actually more meaningful in the effects that your character can do.
That would certainly solve the other issue I have of durations: they're too rigid. I wanted to make a spell that lasted about 6 hours but I only had the option of 1 hour or 1 day. I had to go for a day but it just felt wrong.
I don't want to change the categories as that would also require changing the math - and PL being a ^3 curve, that would mean most effects are out of reach for a very long time.
I don't see the duration category as rigid at all. Consider it brackets. You went right picking "1 day" for a 6 hour effect. Remember that a longer duration is not always better. Basically, the categories are just there for the math part. Nothing stops you from making a spell with a target of exactly 3 humans, either, picking the "group" category.
And yes, the accidental killing is something... well... let's just say one thing we all learn is that pretty much every magician who wants to live will constantly have a few protection spells on him. Since magic can not be detected, that's perfectly fine and not a giveaway. Note that there is no deterioration in spells anymore (I removed the "interaction" part from the rules), so a protection spell once cast is good against many attacks, which should counter the problem of having to constantly waste a lot of energy on refreshing protections.
On interactions, I think a new rule is asked for: We have two basic categories of bases - physical and non-physical. Each should be able to defend against attacks from the same category within reason.
And we have a problem with energy/concentration regeneration. Astalos probably exhausted himself there, but thanks to the whole roleplaying taking a lot longer than the action, he had regenerated some when it was his turn again. Or players could simply wait with posting their next roleplay until they have regenerated enough.
Maybe we need a game mechanic of characters entering an "action scene", which halts regneration, storing everything that would have regenerated and when the character exits the action scene, he gets it all at once (so nothing is lost, but people don't regenerate in game-time seconds what should've taken hours or days) ?