You don't have to think about any of that in BG1. Again, I question whether you've played the game.
The vast, vast majority of enemies that you face do not have any resistance. Kobolds, gnolls, ogres, wolves, regular human bandits (both archers and otherwise) die to everything. It's not until you get to Baldur's Gate proper and/or pursue the dungeon crawl that is Durlag's Tower that you get to any real significant resistance.
And by that point, spell resistance is about as significant consideration as elemental resistance is in DAI or DA2.
Rest was similarly pointless. Once you reached level 4-5 the trash mobs that spawned - gnolls or kobold or ogres - could be exterminated with prejudice by your melee without even needing your clerics or mages to cast.
DAI doesn't have much tactical difficulty, but neither does BG1. We can debate whether BG2's rock paper scissors magic battles were tactical.
Funny, I'm going through BG1 right now.
Every creature in this game has resistance values - minus or plus resistances, but that's not the point. The point is that the combat is resolved by rolls (like die rolls) and there is always a possibility that a lowly wolf will resist your charm spell or this measly kobold will land a huge critical with his axe (x3 damage), dealing a one-blow kill to your squishy mage (who at level 3 has 18 HP max). Obviously they die to everyhing (swords, magic, backstab etc), same as your character. What you're stating corresponds to the easiest difficulty level; then yes, you can streamroll through the game.
If it's such a walk in the part then maybe try the insane difficulty level.
Then come back here and we will be able to have a proper conversation.
Sorry mate, I've spent a good few years replaying both BG1 and BG2 and know these games by heart (still remember some saving throws of particular creatures...) and it seems you just manipulate facts hoping no one will come and catch you red-handed.
Elhanan
Seen your responses in most threads here, and cannot help but notice how you smuggle the history of your life into your responses. First, quit this practice, as it brings nothing to the discussion other than your desire to show how knowledgeable you are because of your history. Let your posts speak for themselves, mate. Second, for a person with such a colorful background, it's a bit odd that you spend the majority of your time (almost 12 thousand posts) arguing with kids. One can assume that you are relatively old (~40), therefore, more than anyone, you should know that wasting time on a video game forum arguing with those pesky kids, and inserting bits of your personal history in your posts is pointless. Third, the personal details (and the diversity of them) create an impression that it's all far-fetched to say the least. Anytime you are losing an argument, you conveniently pull out a personal information card that dismisses whatever the other person said and focuses the attention on you (like you mentioned cancer in one of the threads. Seriously man? You expect me to believe that a grown, experienced by life person would do that?). Sorry mate, but it all looks like a stereotypical guy hiding behind a monitor and the anonymity of the internet, spewing lies about his/her life to show how remarkable his/her life is in an attempt to just get some attention.
On topic; yes, DA:I is one of the worst Bioware games ever made, but it's only understandable - the direction they're heading embraces a new generation of gamers, while leaving the been-here-since-the-beginning fans behind. Sad truth, but they just pursue the money. Hard to blame them for that. To all disappointed people - move on. The gaming industry offers enough to satisfy your needs. I did.
Peace.