on short rest wizard only could replenish their spell slots. what about other casters like divine? only just 1 long rest per day and most caster spells are prepared. i'm not sure what to think of this. its probably means casters should just stay out of range and use their bow/crossbow. only use some buffs or nukes on some difficult battle. also i find some spells duration a little too short which makes caster really not that appealing. anyone correct me if i'm wrong. the shield spell is a reaction and only useful for 1 attack.
Wizards (in 5e and BG3) are long rest casters, just like practically all other casters. Only warlocks replenish slots on short rests. If you're suggesting that Larian rebalances BG3 such that wizards become short rest casters, why not other casters too? If you're just referring to wizard's Arcane Recovery, that's only 1 slot per day during a short rest, which is a relatively small effect comparable to clerics getting their Channel Divinity back.
Warlocks replenish their spell slots on short rest by design; correspondingly they only get 2 spell slots whereas other casters get 6+. Warlocks are expected to expend all their slots between short rests (short-rest-based class) while other casters have to ration all their slots over the entire day (long-rest-based class).
All casters have unlimited castings of their known cantrips, which are likely more powerful than any non-magical ranged weapon given that the attack roll bonus/save DC is dependent on their spellcasting stat while weapons use (presumably lower) Dex. I typically recommend that all casters take 1 attack-roll cantrip and 1 saving-throw (damaging) cantrip for this reason.
The Shield spell lasts until the start of your next turn. It is a very powerful spell: +5 to your AC is huge considering the bounded accuracy of 5e, and you'll never waste shield because you get to know the attack roll before casting it. Additionally, at higher levels your other level-1 spells often become less effective, but Shield remains a powerful option and only uses your (often-unused-by-casters) reaction.