Ive done multiple playthroughs of BG 1 EE at this point...and in every playthrough, having a fighter in the party is simply the superior choice and makes most encounters trivial. Infact, the game becomes extremely easy if you have a fighter/thief and a fighter/cleric as well, as they get the 2 point proficiency bonus, the ability to use longbows (for thieves, this is pretty huge) as well as better THACO/HP.
For most encounters, just having your fighter with some decent gear run in is enough to murder everything. The extra weapon proficiency points are way better than the abilities paladins/rangers get...compare a 9th level blackguard to a 9th level fighter for example. Even with aura of despair, the fighter does more damage. Immunity to level drain is cool, but that can be achieved via other means.
The cleric, mage and thief are basically just there for utility. In my last SOD playthrough, I had a fighter kill the green dragon in two rounds just by throwing some simple buffs on him (haste, chant, etc) and using breach to take down stoneskin. 112 hp doesnt last long when you have a fighter with 4 attacks averaging 18 damage per hit, which you can achieve easily by the end of the first game (19 str with the tome, no half orc needed). Enemy mages die instantly unless they cast stoneskin/mirror image immediately and even that only maybe 2-3 rounds of time max.
The fact that you can have a dwarven fighter with a +7 bonus to 3 different saves at level 1 (if im reading the race description correctly) is also quite silly. By level 9, you have a fighter that is pretty much immune to any spells that let you have a saving throw...without even using potions or buffs.
Theres literally no reason for me to use most of the options in the game because one fighter just slaughters everything. For example, why risk backstabbing with a squishy thief (which requires you to spam invisibility) when a fighter can just run in and kill everything? Its just way easier to give the thief a bow (hence the fighter/thief multiclass) and have the thief around mainly for open locks and find traps.
Its also hard to justify use of damage spells because the fighter makes them largely redundant...unless you just want to delete a dozen low level enemies with a single click. Like...why bother with melf's acid arrow when the fighter can kill the same target in one round?
Even taking out the entire crusader army stationed at bridgefort or dragonspear castle is pretty easy. You may need to pause occasionally to cast chaos but you can pretty much just watch your fighter chunk everything with ease.