Are these the same thing?

General Discussion
1

  1. Gain Immunity to Immobilize Effects.

  2. Control Impairing Effects.

If not, what is the major difference?

2

Not all Control Impairing effects immobilize you. Vortex, Waller, Slow webs, etc.

3

Gain immunity to immobilize effects will prevent things like Jailer and being frozen. Control impairing effects will affect those same things, but will only reduce their duration on your character, not eliminate them. Control impairing effects also respects any DR associated with said effect as well, so will always act accordingly with regard to how much effect something can have on you if DR is present. This should be a non-issue in nearly all cases as a minimum of six seconds between the same effect on your character is enforced to prevent spamming of those effects by different monsters (prior to the six second monster ability effect cooldown, you could be perma-jailed, frozen, or repeatedly knocked back).

4

You might remember the structure of the solution from mathmatics for example.

“Every result from B is part of A. Not every result of A is part of B.”

Like in “rational numbers”, “even numbers”, “uneven numbers”, etc.

Same here:

  • Control impairing effects are ALL effects that somehow hinder/delay activities OR fully prevent activities OR stop/change current activities for something else.

  • Mobility is a specific type of control.

  • There are other ways to control someone/something.

Examples
Replacement (pull / knockback / forced teleports (Wormhole for example)

Fear (losing control: either characer running away, or trembling in fear, on spot.)

… and plenty of other ways.

All immobilizing effects are also control impairing effects; not all control impairing effects are immobilizing effects.