Jvegi Average Manatee I suppose I consider the caster spells moved to 1/day HLA a downgrade because they 1) super powerful and 2) I almost always play a Wild Mage, so they are off limits to Nahal's Reckless Dweomer. Remember that they are only selectable once, so you will only be casting any of them once per rest. No more multiple Planetars, Improved Alacrity or Dragon's Breath spam. I think its a very appropriate change in lieu of no Level 10 spell slots.
I'll agree if you are playing wild mage, but wild mage is already the most overpowered class in the game IMO. For other mages in what I would consider a normal looking party, I'd disagree.
Planetar: you can only have 1 out at a time. They are strong enough that it's really rare for them to die even in boss fights. They also last long enough to be out for several non-boss fights. So I don't think you ever need to really have more than 1 planetar per mage if you have 2-3 mages in the party. So that's 2-3 spell slots saved.
Improved Alacrity: Generally the way I use this is to put on vecna and amulet of power and spam like 30 lower level instant cast spells. You can only do this once before resting, so again not terribly much reason to take more.
Dragon's Breath: It's honestly only slightly better than Horrid Wilting in damage to begin with (horrid wilting also give enemies a penalty to saves), and it deals fire which is one of the most commonly resisted damage types vs. Horrid Wilting's Magic which is one of the better ones. There's also Comet which is almost the same thing. Enemies almost always save by ToB, so both are just 10d10 fire damage AoEs, so you're basically getting 2 fire AoEs for free by making them HLAs. Though I will say its cool when edwin has 7 spell slots dedicated to these and uses improved alacrity to unleash them all in a single frame.
And there's many excellent level 9 mage spells to use instead like imprisonment, wish, spellstrike, black blade of disaster, and time stop. I don't get the argument that getting one of the each of the above for free + using these is a downgrade.
I'd actually say it's clerics/druids who are hurt far more by making HLAs one-use. Implosion and elemental summoning are really, really good spells compared to the fairly lackluster level 7 spells divine casters get. And divine casters end up with a lot more level 7 slots than mages do level 9 slots.
PS: I like the scribe scroll feature. No longer are you starved. The scarcity of some spells is a detriment, and it's nice to be able not to have to literally book keep which mage has what. Scribe scrolls isn't cheap and is a very legitimate D&D function.
I just read the component, I don't know what the cost is. But I know by the 2nd half of SoA you have almost unlimited money and millions of XP, so I'm assuming the cost doesn't matter then. I do get that it's a PnP D&D mechanic but there's a lot of things that make it sound really abusable in BG2.