The new system is more restricted because one very important variable is taken away.
You cannot have cheap spells anymore.
What happens to midnight oil? It has to compete with spells of higher order like earthquake or chain lightning.
What do you do to save it? Is it obsolete mid game? Always burn it because burn deals immense damage? Don't burn it because the slow is so immense melees have no chance reaching anything in their lives? Don't burn it because it deals damage and has a significant slow?
Chain lightning is simply stronger than a plain lightning bolt. In the old system you could decide to use less ap for a spell of similar or worse reliability because in case of success you had options to either capitalize on it or try another disable because there is one target more important than the others.
In the new system there is four possibilities: use 3x1ap, 2+1 ap or 3 ap moves or spare a point.
(With more ap an ogre could wait a round and simply club one char of choice to death.)
If chain lightning has less than 3 ap cost, lightning bolt automatically becomes a second class spell. If chain lightning is strong enough to be a 3 ap or even 4 ap spell, having another even faster char with the ability to haste that one will push chain lightning into the mandatory opening strat trivializing most encounters.
RNG makes little sense in a 3 ap environment. One char cannot set itself a goal and invest more or less effort into slaying one foe. If there is one miss it costs at least 33% of your dps, if not your whole strategy because the sole attempt already ate up your ap. The alternative is a game where it is hard to tell if a move was a good/better choice because it will be a gamble either way.
My main concern is that most spells will need a self-contained purpose and balance which in turn will equalize most of your choices.