Re:
How can a mechanic be disconnected from a game world in the absence of a group of people creating a game world and attempting to use the mechanic according to their preferences, priorities and experiences?
Let's pop over to a favourite game system of mine for a minute: Champions
In that game systems all abilities are created by the player from building blocks and all abilities start off disassociated.
Character A has a 9d6 Energy Blast (EB). Mechanically, it is mostly defined. When character A succssfuly targets an opponent, he rolls 9d6 damage. We need to add more more piece of information to complete its mechanical association -- what defence the victim applies to the damage. Let's say is Physical Defence (PD).
So character a has a 9d6 EB vs. PD. There's a mechanical definition of the power.
So how is character A's ise of the power in the game world described? Does he throw his hand at people? Does he issue a massive shout? Does he fire bean bags rounds from a gun? Perhaps its projectiles of raw kinetic force?
The next step for character A is to associate how the mechanical ability of 9d6 vs. PD fits in the game world. Some of those associations will impact how effective the ability is and mechanically the cost of the power will change - perhaps he fires bean bags from a gun -- so the gun can be lost, there are only so many shells carried, and so on. Perhaps it is projections of magical force that slams into the opponent that are invisible to the naked eye, but can be perceived by those with magical senses.
Other associations don't affect the value of the power, but affect how other powers in the game will interact with it -- is the ability magical in nature and as such suppressable/dispelable? Does it require an electrical supply and thus can be negated by anything that can stop electrical transfer?
Further associations are how the ability manifests -- what does it look like to third parties -- this helps guide how those observers react.
So a 9d6 EB vs. Pd can be anything from bean bags fired from a gun, magical bolts of invisble energy, concentrated spray of high-pressure water, or any other effect in the game world tha the player can describe that will fit the mechanical description.
So let's see how we can model Come and Get It shall we?
The fluff suggests it should be a charismatic ability, but there are no limits to the sort of creatures can be taunted, teased, or otherwise convinced to come to the character.
Perhaps a mental ability? But there are no restrictions or differences between pulling a close melee combatant that would naturally pleasd to get close and a creature whose only ability is ranged combat and should be deathly afraid and complete against getting that close.
Probably the best match is a small area telekinesis. This will affect most opponent types (to affect ghosts and such will require mechanical advantage), can be limited to the just pulling the opponent into position -- but now we must deal with the lack of mass limitaiton. Let's sidestep that for the moment and go with telekinesis. So what is the in-game justification for the ability -- the power source as it were. Martial. So puissant skill at arms and strong martial training lets the character telekinetically yank opponents into range to be sliced with the melee weapon. Maybe not.
OK so possibly it's not a power easily modeled in the other game system.
Perhaps we won't associate the power with the game world just yet and say "The player will associate the power at each use choosing an association that makes sense for that opponent within the constraints of a martial ability."
What does this do? It leaves the abilitiy disassociated with an implicit contract for the player to fill in the blanks as best he can; sometimes its a taunt, other times it's the opponents getting over-confident and just charging forward. It stops being a single thing and becomes a situation common to the character. There is no consistent reason opponents get so close to the character; it just happens as a matter of course. The player is affecting not only his own character, but the motivations and actions of the opponents affected by the power. What happens when the player gets lazy, distracted, or just can't think of a rationale that applies right now? The ability gets used bare or someone steps in and says "No it doesn't work this time."
Imagine that I'm a "lazy" player. I don't want to continually rationalise why my opponents make this tactical error. So I say (with the appropriate dice rolls) "I use come and Get It and move the opponents from here to here and they take this much damage." In what way is that asociated with the in-game fiction? We see the results, but not the cause.
You may call it bad play; it most likely is since the player agreed to to implicit contract when he took the power. Despite that, it is play that sound under the rules of the game. RAW vs. RAI.
) It remains to be seen whether 5e can somehow steady the whipsawing between G and S, and successfully hybridize the two in a game that still hits "D&D" for most people. 
