That's the one? The one that is literally "get a +3 to attacks and damage" is the one you think is the edge of magic?
If it turns your sword into a magic sword, it is the result of magic.
And honestly, why not just give the fighter a straight increase in attack and damage rather than turn their sword into a magic sword?
Because they are that good of a thief. Seriously, it isn't hard. Stories have been doing this millenia. And frankly, immersion can go die in a hole. Because immersion is what keeps martials locked down and "normal" while we let casters get away with anything. I'm frankly sick and tired of immersion and realism. That's for levels below level 15, after that you are a multiversal force, you should at least be capable of breaking simple human limitations.
"It's magic" isn't really an explanation for how you can alter reality on a whim without tearing things apart, it just shuts down the conversation. "They are just that good" also shuts down the conversation in the exact same manner.
"As the paladin falls, decapitated, the cleric runs to his side. With tears flowing down their face, they begin casting a spell and in a flash of light, the paladin rises with his head intact. Weakened, the cleric falls to his knees."
"How did you do that?!" The rogue player asked.
"My deity saw my faith and answered my prayer. With divine intervention, they were able to heal."
Vs
"As the paladin falls, decapitated, the rogue runs to his side. With tears flowing down their face, they begin to pull out their surgical equipment and in a few moments, the paladin rises with his head intact. The rogue swipes sweat from his eyebrows."
"How did you do that?!" The cleric player asked.
"Oh, I'm just
really good at medicine."
...
Nah, sorry, can't do it. That'd just kill the moment.
And unless you mean "reliably succeed without rolling a die" then you are falling for the same trap we are always dragged into.
This is what I mean, yes.
You mean.... all of them? There isn't a single spell that doesn't "just work"
90% of spells that inflict a status on the enemy requires a save.
A lot of spells require sight.
A lot of spells require targetting.
Commune has a chance to fail.
Teleport has a chance to fail.
Power Word Kill can fail.
Gate can fail.
Illusions can be seen through.
There are wards, barriers, and areas that can cause spells to fail in general.
There are spells dedicated to making spells fail.
There are many ways spells can just not work, but those spells are considered "bad" because they aren't guaranteed and only the spells with extremely good effects are even considered.
But here's the thing. There is a reason that WoTC got rid of those things... they sucked! No one liked them. Those that did, kept playing those editions.
And we don't need to nerf the casters, we CAN. BUFF. THE. MARTIALS! It is allowed. Perfectly legal. Not a crime.
Apparently, we can't buff the martials. There's a certain threshold people are willing to let martials be buffed before the casters start having a fit.
And maybe we shouldn't baby casters. If they want to be able to control the fabric of reality the least they can do is understand that power comes with drawbacks.