What realistically limits higher spells is a from my DM-PoV is the time frame of BG3 which is not even a month. Yes, in the game scrolls just poof into your spell list when you learn them and you can pick new spells out of thin air when levelling up, but at least in earlier AD&D-rules learning a 6th level spell would have meant booking lots of lab and library time.
To be fair, that's only the case for Wizards.
Sorcerers, Clerics, Druids, Bards and Warlocks don't need to actively "Learn" a spell. At best you can consider Clerics, Warlocks and Druids needing to attune to their spell lists. Maybe Bards need time to write their songs (Sorcs are kind of just weird and abruptly develop spells based on their bloodline)
That said, there's also the whole thing in the lore about how the characters have been "Deleveled" by the tadpole. It being outright mentioned by Wyll and thus presumed to be the case for others (Especially Gale. His whole backstory was that he mastered all of the Weave mortals had available and that he wanted to go into the forbidden areas of the Weave to explore more of it... Which suggests he knows more than just a handful of cantrips and level 1 spells...)
So potentially you can factor in characters recalling or regaining access to prior abilities from leveling up. This can include Wizards too, as their spellbook would still contain all the spells they've written down. They just need to get back their mastery of the Weave in order to channel it into those spells. Whereby "Instantly writing a scroll into the spellbook" could be considered just
eating reading the scroll to quickly refresh the memory of how to manipulate the Weave for that spell that was already in their spellbook.
And while the game technically allows you to do it in your backpack while walking, I also avoided creating potions unless camped or at least in a discovered lab and always collected lab gear to have a lab corner at the camp.
I did that too. Though to be fair, it was less about the lore factor of things and more because I had a dedicated potion maker as a camp attendant (1 Rogue/2 Transmutation Wizard) for Medicine Expertise and Experimental Alchemy class feature. Sometimes I also multiclassed them into Cleric for some of those extra buffs (Light, Aid, Protection from Poison, Deathward, Freedom of Movement)
Though, it did always seem somewhat lore friendly to have a camp steward. Someone who travels with the group to set up the camp, gather firewood, prepare meals, dabble in potion making and the like. Affording the adventuring party more time to focus on adventuring and less time on all these mundane tasks.
Withers doesn't strike me as the sort who's really big into the whole "Manual labour" aspect of camp maintenance...
