BG1&2 don't let you equip two handed weapons, ranged or melee, in quick slots if you have a shield equipped. And it feels really good to play a Greatsword fighter who can quickly switch to a Composite Longbow and have that melee/ranged flexibility after giving up that +2 or better AC from a shield.
If you're thinking of the fact that the original games didn't let you equip a shield if you wanted to have, say, a longsword and crossbow in your quickslots that annoyed me so much! Thank goodness they fixed it for the Extended Editions

.
Also worth mentioning again that the quick slots in BG3 should not be restricted arbitrarily to ranged and melee. You need to be able to equip combos like Sword+Shield that you can switch to Hammer+Shield when you need blunt damage. And rely on thrown weapons for ranged.
Sorry if this is old news to you, but I only realised this patch that the game does seem to be trying to give us a way to quickly swap weapons, though it is either very buggy or I'm just using it wrongly. But it's fine if you just want to swap between similar setups like sword+shield and hammer+shield. You just drag the weapon you're not currently using to, say, custom slot 1 in your toolbar, you can then use that button or the 1 key to toggle between hammer+shield and sword+shield. This takes an action, which is still instantaneous outside combat and is arguably fair enough in combat (depending on your overall view on weapon switching). If you want to swap between weapon+sword and a two handed weapon it works less well, as you lose your shield when you toggle to the two-handed weapon and so need to also map your shield to, say, slot 2. It then takes two actions to re-equip your one-handed weapon and your shield. The problems really come if you're trying to set up multiple weapons rather than just toggling them or are dealing with dual wielding - either the game gets really confused, or I do, or both.
Still, at least it's the start of some functionality that could hopefully be fixed.
Apologies if I'm not understanding you about thrown weapons, but if you are saying they should be equipable then, given that you need to go collect them after every fight then it would be a pain to have to redo this every battle. Choosing and throwing a weapon at the moment, without having to equip it, seems pretty straightforward, given you just press X or click the thrown button and you'll be shown all the weapons you have with the thrown property (well the first time you might need to specifically pick the weapon icon, but this seems to be a stored preference so you then don't need to do that again unless you throw something else), select one, click where you want to throw. It's the picking the blasted things up afterwards I hate.
And I guess this is why we need to be left with a free swap between melee and ranged weapons unless the thrown mechanic is changed significantly, as a melee character can freely choose a weapon to throw from their inventory, and be left still holding their sword and shield afterward, so it might be unfair on ranged characters not to allow them the same. And if they can freely swap between melee and ranged, then you may as well give any +2 AC bonus permanently as all it really does is remove the busy work of swapping back to the melee setup at the end of each turn (damage incurred on the player's turn excepted, I suppose). Of course, you could make it so that it takes an action, or a bonus action, for a melee character to swap between melee and throwing, but I think I'm starting to see why Larian have done this the way they have! Sorting it out in the way I'd like is starting to feel as though it would require some reasonably big changes to the interface.
It's worth mentioning that it is only free to switch between melee and ranged weapons which I am totally fine with. It'd be a serious pain if switching those cost us an action. It is worth mentioning that it does cost you an action to change your melee weapon to another melee weapon or an equipped ranged weapon to another ranged weapon, which I also think is fair.
As a result of thinking through how thrown weapons currently work and what interface changes might be needed to handle them differently, I think I might be starting to come round to this view, at least from a practical point of view. Hmm. I'm not sure. I'm going to have to think on this more deeply.