There is a route upward for slaves to integrate into society, but they're not going to then become holders.
Actually, this is one of the biggest misconceptions, ever: The Udorian Tash-Murkon family, who isn't only a family of holders, but a royal family, started out, being Udorian, as slaves. Many Udorian holders stem, probably, from families that were enslaved, once, the same is true for the few Ni-Kunni holders.
I also don't buy into the argument that how Matari handle being outcast is something 'very Caldari'. It might be from a certain perspective but about everything is from a certain perspective like something else from a certain perspective. The trick isn't looking from the perspective that makes things look alike when you want them to look alike and to look from the perspectives that make things look not alike if you want them to not look alike, but to look at things from several perspectives to begin with to approximate a more objective point of view.
So, yes, if I think about it
like that then the Matari and the Caldari seem very similar, but unless you want to advertise for this way of thinking about it (which you gave little reason for, imho) it's not a good argument for how the Caldari meritocracy fits with Matari tribalism, as it ignores other ways to think about it and avoids to engage those.