Where I say give me mechanics that do the specific things that need doing in that instance, and if it ends up being complex (particularly on the DM-side) then so be it.
As a player, sure, I want it simple. Mechanics get in the way of roleplaying.
But as a DM, I want it as complex as it needs to be to give granularity in resolution and at least vaguely wave at reflecting reality - or at least being able to reflect the in-game reality - halfway consistently. Therefore, I-as-DM expect to be laregly dealing with those complexities so the players don't have to bother with them as much.
What gets sacrificed, every time, on the twin altars of simplicity and speed are granularity and detail; and while it's also certainly possible to go too far in the other direction and end up with a game that loses itself in details, 4e and 5e in their rush to simplify have IMO lost a lot - as in, far too much - of what makes play interesting.
Interesting to who? The DM? The Players? The Table? Because, AFAIC, the loss of that granularity and details has resulted in a massive improvement in game play. No more one hour of fun packed into four hours.
Every iteration of D&D has filed off all that granularity to some degree, from going from 1e to 2e and losing the weapon vs armor tables. Actually, there's a pretty good analogy of why simplicity is a good thing. In 1e, if you actually played by the rules, it was largely impossible to actually run combat. There were a thousand little rules - who had higher ground, if the target has a shield or not, never minding trying to determine the weapon vs armor for monsters that didn't wear armor but still had an AC or had an AC that wasn't on the table (as in anything less than a 2 AC). It was a huge mess.
Now, most of the time, no one actually used the rules. They used something that probably vaguely looked like the rules, but, they certainly weren't following the actual rules in the book. So, 2e comes along and simplifies a lot of the rules. Shields just work. Still some situational modifiers like higher ground, but, the weapon vs armor table is shrunk down to three types - piercing, bludgeoning, slashing. Then 3e comes along. Weapon vs armor goes away because, again, it was too hard to use in play - there was no mention of what to do with monsters that don't wear armor so, largely, the rules just got ignored. Also, different damages vs size of target goes away too because, well, it's a PITA (is something 7 feet tall large or medium?) and led to all sorts of rules wonkiness (why, exactly, is a longsword twice as effective against a giant as an axe?). 5e takes it even further - no more flanking bonuses, movement calculations don't use 1: 2:1 counting. That sort of thing.
There are very, very good reasons why we reject complexity in the game. It really didn't add anything to the game because so many times, any time you had these complex little sub-systems, the sub-systems were either used incorrectly or flat out ignored.
Which rolls us back around to the magic system. I get it. I really, really do. I REALLY would like to do a low magic D&D campaign. It is possible, but, requires a huge amount of buy in from the players and largely means you're going to chop out 3/4 of the game. Which, at that point, it's probably better to run a different system because, well, it will just work better. But trying to add back in all this granular complexity in order to make the game more "interesting" just doesn't work. We've got decades of game play that proves that it didn't work. If it did work, we'd still be doing it. So, we simplify. Which, in 5e, means leveraging the spell system. Anything that's not 100% mundane becomes a discrete spell (or something that is exactly like a spell in all ways, but, just not called a spell) with a discrete rules package that is very easy to reference in play.
