Physical attacks based off a high stat have exactly the same chance to hit as spell attacks with the same value in the spellcasting stat. If anything, it's easier to hit with firebolt/ray of frost because these still hit the ground even if you miss. If you have a lower chance to hit with firebolt compared to a crossbow, then your ability scores are probably way suboptimal.
This is not necessarily true for ST spells, because enemies have different ST bonuses than AC bonuses. So, if by "certain type of spell" you mean "spells that affect STs," then yes these can be more difficult to hit. Especially since you don't get high ground bonuses to these spells. ST spells are weaker in BG3 than melee/range/spell attacks.
Until Larian rebalances the game so that ST spells are equally as powerful as other spells, I'd suggest sticking with spells that are attack rolls instead of ones that force STs. This will make your wizard feel more powerful (if more limited).
Mage armor gives you a higher total AC than any nonmagic light armor. Whether you're in light or no armor, you still add your Dex to your AC.
--Wizard with Dex of 14 and mage armor: AC 15
--Warlock with Dec of 14 and studded leather: AC 14
I agree that it is very immersion breaking to rest after every fight. Especially when the game and companions are urging you to find a solution.
