The core problems with a larger party:
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a) In BG1+2, especially on high levels, you needed two tanks, two healers, and two wizards, because you would quite frequently be attacked from two sides.
And on highlevel the routine was: the wizard gave the tank Improved Haste, the healer gave the tank Regeneration, and the tank would attack the moment he got these two buffs.
That was because AC didnt do much on highlevel anymore. This wasnt fixed in D&D3 either and was only finally fixed in D&D5. Unfortunately I would have to argue that D&D5 fixed it too well and now we have the problem if you really invest in AC you hardly get hit anymore at all.
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b) Another problem why you had to have a larger party in BG1+2 was YOU HAD TO HAVE A THIEF.
Both AD&D and D&D3 literally forced you to have a thief in the group, otherwise you would be helpless against traps, and locks could be a huge problem as well.
This was a horrible misdesign that also got finally fixed in D&D5.
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c) Once you have figured out combat in BG3, it is unfortunately most of the time completely centered around 1. going first and 2. killing or disabling the opponents before they can act.
The abilities of the opponents are just too awful to tolerate allowing them to trigger, and going first/disabling the opponent is very doable.
This completely destroys the need for any sort of strategy for many later battles.
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d) Furthermore healing is a complete PITA in this game. There is no equivalent to the Regeneration and Heal spells in past iterations. Even the best healers hardly manage any healing at all, and getting healing potions is also not easy.
Your best bet in this regard is playing classes that simply negate most damage. Which ironically is also a possibility - Wildheart Barbarian (7), Bear, Stallion, with Thief (5) for a second bonus action (so you can refresh the temporary hitpoints every round) and Uncanny Dodge, and then linked to an Abjuration Wizard.
But really the easy strategy here is mostly just doing ranged damage and avoiding getting hurt at all in the first place.
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So the bottom line is BG3 just doesnt need a bigger party, because there is such a simple basic strategy that almost always works. Which is a very sad state of affairs.
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What do I personally want from games like all three Baldurs Gate games ? A group of characters, each with a couple douzen abilities, where I have to actually think what ability to use next. BG1+2 gave me that on some spellcasting classes (Mage, Sorcerer, Cleric, Druid), but there was no such complexity for warrior classes.
Its basically what WoW offered, combat wise, though they made IMHO some very poor choices, like allowing people to completely reskill their characters to different party roles. Vanguard: Saga of Heroes offered this really well, especially in the late stages of the game, however its gone now and people dont even seem to know anymore why it was so great (awesome class design, awesome dungeon design, awesome raid design, a huge game world with realistic viewing distances and no instancing - a classic MMORPG "done right").
D&D5 has fixed some important shortcomings of previous iterations of D&D, but the fun the Larian game devs had with playing around ended up in a strange place where you have an extreme amount of choices but many are objectively quite meaningless, because winning Initiative and killing the opponent with spike damage or disabling them with spells is the dominating superior strategy.
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