Would you say that the difference you’re bringing up is about what’s important to the specific character? That you want for the game to be about the characters and their desires rather than just feature them?
Yes,
in that context. I'll explain the qualification by way of an example from a specific system.
Each PC in Marvel Heroic RP/Cortex+ Heroic has two
Milestones. Here are two example milestones - one is from Captain America in the core rulebook, the other is one that I made up in collaboration with the player for the berserker in my
Cortex+ Fantasy Hack Vikings game:
MENTOR THE HERO
1 XP when you choose to aid a specific hero for the first time.
3 XP when you aid a stressed-out hero in recovery.
10 XP when you either give leadership of the team to your chosen hero or force your chosen hero to resign or step down from the team.
WORDS, NOT DEEDS
1 XP when you begin an action scene with a non-attack action
3 XP when you inflict emotional stress or take mental stress via an argument
10 XP when you either foreswear conversation as useless (“words are for women and lovers”) or when you foreswear the initiation of violence
There is no limit (other than inherent constraints, like you can only do something for the first time once) on how often you can achieve the 1 XP milestone. The 3 XP milestone will only accrue XP once per scene, even if repeated. When the 10 XP milestone is completed then that particular character arc is done, and a new milestone is needed. The WORDS, NOT DEEDS milestone was taken up by the berserker in my game after he'd completed his initial DEEDS, NOT WORDS milestone (because
an impulsive action caused him to be stressed out, which was one of the options at the top of that original milestone).
The feature of these milestones that I want to point to at the moment is that
a player can play them, earning XP somewhat independently of what the GM is serving up. Not completely, but somewhat. (This degree of independence can also vary a bit between milestones. I've chosen two examples that clearly illustrate the point.) I think this is a deliberate feature of the system, that reflects its starting point as a supers system - it tends to detach the character arc from the details of the practical ingame situation, just as Spidey's character arc will tend to progress whether it's The Vulture or Sandman who features as the villain in this month's issue.
But the system also has mechanical features that support these milestones. For instance, taking non-attack actions in action scenes, including aiding other heroes, isn't the sort of sub-optimal choice that it often would be in D&D - conflict can be won by attrition but doesn't have to be, and building up assets (which are generated by aiding others and/or taking non-attack actions) is one way to establish a dice pool that can allow a one-shot victory rather than require attrition.
So it's pretty hard for the GM to
actively get in the way of the players exploring and playing out their milestones in the course of engaging with the GM's material.
Now to bring this back to my AD&D 2nd ed experiences: obviously there's no
mechanical subystem comparable to the Milestone system. But, in play, we as players would develop our characters in interaction with one another and these arc-potentials would emerge somewhat organically. However, in AD&D it's incredibly easy, I would say almost to the point of inevitability, for the GM to get in the way. For a start, you almost always have to subordinate this stuff to more pragmatic considerations once the action starts. And the GM has such a high degree of control over aspects of the gameworld that player action declarations become very dependent on what the GM has put there.
So I think,
in an AD&D context - and the same is true (I would say) for Rolemaster, 4e D&D, and I would expect 5e too - that in practical terms
the GM not getting in the way turns into
the GM brings up stuff that is important to this character. These systems just don't support leaving that to occur on the player side.
I hope that makes sense, though it really only scratches the surface of this particular topic. (Eg MHRP/Cortex+ at least in my experience isn't an ideal vehicle for
intense play for the exact same reason - there's a "background-ish" aspect to the GM's material relative to the PC story arcs. I think intense play wants these to be more tightly connected (necessary but not sufficient condition). But not all protagonism has to be intense protagonism.)