Call me an oinky-pig if you like, but I want both groundedness (which you define really well in the bolded, I like it!) and verimisilitude/realism.
But you include magic in your games. There is no "veri" to have "similitude" when it comes to magic. There is no "realism," because
magic is not real.
IMO the way to (try to) achieve both is to (behind the scenes) expand real-world physics principles into the fantastic such that the setting physics can usefully underpin everything. IME once that's done, keeping one's explanations and narrations consistent becomes much easier.
But that is the very process of groundedness--not realism. You are not forcing magic to conform to the laws of Earth physics; you are laying out new, fictional laws of physics which
replace them. You are creating the new ground upon which a foundation may be built, with the intent of allowing naturalistic reasoning to hold sway. If ever realism--conformity to the way our extant physical world works--actually conflicted with these new, established laws of fiction-physics, I'm pretty sure you would not simply chuck out those established laws without a care!
I mean, for example, instantaneous travel and/or communication necessarily results in
time travel in a reality where physics works like it does IRL. (In layman's terms, because of how information propagates through space, being able to instantly move from one place to another allows effects to happen "before" they were caused, from at least some points of view.) And these things are not some distant phenomenon no one can observe. The color of gold is what it is because of general relativity: the outer electron orbitals of the gold nucleus are so large, they start suffering measurable time-dilation effects, which distorts their emission spectrum into being (very slightly greenish-)yellow rather than the typical silvery color of metals. Silver is also big enough to experience some relativistic effects, but human eyes can't detect them; if we could see more short-wavelength light (as some tetrachromats can), silver would appear to have color, effectively "anti-ultraviolet" (since it absorbs ultraviolet radiation while reflecting essentially all visible light.)
But I'm sure this doesn't prevent you from including
time stop and
misty step in your games. Instead, you most likely wave off relativity, because that's weird esoterica for physics nerds (I can say that, physics is my field!), and being able to use classic magic like
plane shift and
teleport is more important than perfect fidelity to Earthly physics.
Or, to put rather more fine a point on it: If you had a player tell you, point-blank, with citations and everything, that something in the game clearly violated the laws of IRL physics, which would you choose: to modify the game world to remove the violation of IRL physics, or to dismiss the IRL physics and say "well, that's just not how
this world works"?
If I were a betting man, I'd put money on you picking the latter in the (significant) majority of cases. It would take an utterly egregious violation of really basic, intuitive physics* to swing things the other way. Because what matters most is the coherence of the system to itself and the ability to use intuitive naturalistic reasoning,
not the coherence of the system to our physical world. Only a really serious breach could muck up that intuitive naturalistic reasoning--and the correction would be undertaken to restore that ability. That it would happen to cohere better to our understanding of the physical world is at best a happy accident.
*Note, "intuitive physics"--sometimes AKA "Aristotelian" physics 'cause he wrote it down and his writings survived--is usually quite bad. Like, actively wrong in lots of ways. But repeated tests of physics students show that Aristotelian physics is how humans intuitively think reality works, even after they've been taught actual physics, if you just give it 6-12 months and then test them.