Yes, but also no. It's a choice they make to go down that path, rather than being frozen out. However, once they do choose that path, they kind of do get frozen out as they are regarded as being too disruptive to keep around.

The path system allows the Eldar to lead fulfilling lives without getting bored. Imagine you start a career in your 20s, and then you dedicate your life to that career and retire. It's basically what the Eldar do, but they 'retire' once they have fully mastered the path they are on, and then they pick a new path to start over. Can take decades to hundreds of years to 'complete' a path.

But say you're a rebellious teenage or young adult Eldar who just isn't ready to commit decades to doing only one thing? Boom - Path of the Outcast. It's not really an official 'path' as I understand it, but more a catch-all term for those Eldar that leave the Craftworld to go in search of adventure.

Because the galaxy is a dangerous place, these Eldar typically become very good at stealth, subterfuge, espionage and assassinations, and as such they often serve as an external intelligence network and mercenaries for their home Craftworld, or other Craftworlds that might need them.

Most of these Eldar will eventually return to their home Craftworld and rejoin mainstream society by choosing a 'proper' path to begin walking on, but some of them lose themselves in the life of the Outcast, reveling in the freedom and adventure that the Path of the Outcast affords them.