Serious question : In the PnP, aren't the spells that targets AC used less often at higher level when characters have higher level and more powerfull spells that require a ST ? It's something Saito brought in another thread and I found interresting to think about (as the non PnP player I am).
I mostly brought that up because later spells that target saving throws will inflict half damage if an enemy succeeds the saving throw against it. Spells that target enemy AC do not have a similar function. As the field effects have already taught us, having sources of guaranteed damage is *powerful* as hell, especially if they are also AoE effects. This type of principle is why spells like Fireball and Lightning Bolt are so feared (aside from those two spells inflicting more damage than other level 3 spells for 'tradition' reasons from the earlier DnD editions). Subsequently it's also going to be why having proper counterspells is going to be extremely crucial.
When Bard is released, pick up the Shatter spell. That's one of the few saving throw spells that inflicts half damage available in the EA right now (and the only ranged AoE saving throw spell right now IIRC), and watch as entire packs of enemies melt under it. My Bard mod playthrough with Gale and Wyll also using Shatter basically melted fights with big packs of enemies with lower HP.
(Bards also get an exclusive 1st level spell called Dissonant Whispers that also targets a saving throw, though it is a single target spell. Currently, if an enemy fails the saving throw in BG3, they are also frightened. The tabletop variant forces them to immediately spend their reaction trying to get away from the Bard instead.)
I don't believe Heat Metal is in BG3 yet either, but it most likely will be eventually, once item tags are sorted out. It's an extremely unique 2nd level concentration spell available to Bards and Druids that inflicts guaranteed fire damage against enemies using metal equipment, and you can spend a bonus action each turn to cause that damage again. It additionally forces enemy attacks to have disadvantage until the effect ends, either by the caster losing concentration or the target dropping the affected equipment (and the spell forces them to do so if possible unless they pass a constitution saving throw - but even if they succeed to retain their equipment, they still take full damage from the spell itself). Though 'dropping equipment' only realistically applies if weapons, shields, or accessories are targeted, which is a great way to disarm an enemy. If your main goal is damage and perpetual disadvantage, you target armor instead.