The D&D spell-slot magic system is a great, efficient system does a number of things that is important for story, pacing, and functionality:
- You get to do things FAST, often as an action, where if you did it in a a mundane fashion, it could take an hour or days to do.
- You get to bypass a lot of mundane physical material components if the act requires construction.
- The effect is usally very accurate and/or efficient, not requiring a skill check for failure.
- It is a system that allows multiple classes get access to these abilities as an option.
- Spell slots introduce a limit for how often you can perform those actions in a day. Because they are slots rather than dedicated to each specific concept, you get to mix and match. If the DM has a subsystem that also lets you do this stuff in a mundane fashion, that would be on top of the spellcasting slots.
And regarding your comment about "just a thing normal people do," I will contest that claim. Let's look at the level 1 Ranger spells:
- Absorb Elements: Pure magic. Not just a normal thing.
- Alarm: Casting time is 1 minute and lets you set an alarm that covers an entire 20-ft. cube that is smart enough to not trigger from allies, and awakens you with an inaudible ping if you're within a mile. Not just a normal thing. Sure, you can do something different, like letting the ranger ask if they create a mundane tripwire/clattertrap, but that all needs context for location, materials, and time. That is too much bookkeeping for designing accurate, meaningful system that I don't think is worth creating. Therefore in my game a player doesn't need an "class ability" so much as a player asking to do it and as long as they have the means, I give a timeline and ask for an ability check, and I'd likely allow Survival proficiency to apply.
- Animal Friendship: Can magically charm one beast per spell level for 24 hours, pending a Wisdom save, using only an action. Not just a normal thing.
- Beast Bond: Telepathy. Not just a normal thing.
- Cure Wounds. Magical healing. Not just a normal thing.
- Detect Magic. Pure magic. Not just a normal thing.
- Detect Poison and Disease. An action to determine the hazardness of everything within 30 feet at a glance, without a touching it? Not just a normal thing.
- Ensnaring Strike. Magical attack. Not just a normal thing.
- Fog Cloud. Big magical AoE. Not just a normal thing.
- Goodberry. Magical healing food. Not just a normal thing.
- Hail of Thorns. Magical attack. Not just a normal thing.
- Hunter's Mark. Not just a normal thing due to the divinatory aspects that work even if the creature is unfamiliar to you. I suppose it could have been a mystical primal-energy-powered class ability useable X times per long/short rest. But we're already past that point.
- Jump. Not just a normal thing, despite the boring name that matches an act that anyone could do.
- Longstrider. Magical movement enhancement. Not just a normal thing.
- Snare. Not just a normal thing, because it only takes a minute to cast, doesn't care about terrain (doesn't need trees) and is "nearly invisible" no matter the terrain. A mundane snare trap requires all those things. That said, it still sucks. I say make it cost an action to cast so you can use it while you are being pursued. That fixes it for me.
- Speak With Animals. Pure magic. Not just a normal thing. I suppose you can make this a class ability, but would bards, rangers, and druids all get this class ability?
- Zephyr Strike. Magical attack. Not just a normal thing.
So... Alarm and Snare are the ones that are the most mundane. Sure, someone can make a subsystem for traps. Maybe I'd take a look at it. But these spells do it quick and reliably, near
invisibly, compared to a mundane option.