Personally, I have no problem with enemies with different vulnerabilities and strengths, but am not sure swapping weapons should be made less costly. Perhaps as a feat? Not sure if there are any relevant 5e rules? I believe that it is consistent with 5e that by default swapping a weapon in a hand takes an action, so BG3 is already being more permissive by letting us swap between a melee and ranged (or thrown) weapon without using an action, which has certainly been the subject of debate here before.
So, formally, you get one free interaction per turn - this free interaction is usually bundled with something related to it, and the most common one is drawing or sheathing a weapon. You get one for free - after that it takes an action.
This means that an unarmed person can draw/equip one weapon, and then attack with it on the same turn, but they cannot draw two weapons, or sheathe a weapon and draw a different one without using an action. You can drop what you're holding for free, if you really need to switch weapon and still attack, but that is dropping it and you'll need to pick it up again later.
There's still a reasonable amount of flexibility in this. For example... My level two barbarian has a short sword and a shield, and throwing axes on her belt. She can leap from hiding and stab a goblin through the chest, leave her sword buried point first in the goblin/ground there, pull a throwing axe (free interaction) and use her bonus action to throw it at the second goblin ten feet away; Next turn she can grab her sword (free interaction) and attack a new target with her action (and when she gets shield master at level 4, bonus action to shield-shove the next one prone). All perfectly legal by the book.
There exists a feat to support two-weapon fighting that lets you draw or sheath two weapons at once for your free interaction.
It may be worth noting here, that two-weapon fighting in particular has always been a little clunky in 5e, and the changes they propose in the oneD&D tests actually do look like they give it some much-needed love and smoothing.