I think people should judge a "meritocracy" with the same jaded and cynical eye they would look at say a "democracy". Both of them can easily be manipulated by the Powers That Be to maintain a stranglehold on the leadership of a society. Again, if anything, it would be far easier to subvert a meritocracy.
I agree, though ICly this is the very reason Aelisha likes the State - as a capsuleer with access to social, mental and perceptive augmentations of the highest order, she can have much higher station and impact in the State (even with their segregation of capsuleers from society at large) than she could in a democratic, tribal or oligarchical/monarchical nation.
As for Sol, well growing up in the system means that even wen you identify with the flaws, it's tough to see the alternatives as palatable (especially when that government made you immortal, rich and generally enabled your progression).
As for players, I think that many of us, myself included, are guilty of drinking our own IC koolaid a little, but tbh I find this is healthy for the community, as most of us, even when guilty of such, can put it to the side for the sake of discussions like these. A bit of OOC passion for a faction goes a long way to building a believable character imo, so long as you don't go full method and start thinking that there is only one true way.
It is for this reason I enjoy Seri's patriotism, Kim's racial/cultural supremacy rants, hard line U'K and Amarr loyalist press releases and the likes. What comes after the statement of intent may be the usual back biting and nonsense, but the hard line aspects or the factions really do provide the skeleton for progressive movements (or practicals in my case) to build around/on/through.
As for the main topic, the Civire/Deteis divide is, as a few have already mentioned, something I feel is culturally ingrained despite the 'meritocracy'. I doubt there is a conspiracy to keep Deteis at the top, as such racial favoritism would become apparent within a few generations as education standards for other ethnic groups fail to rise, but there is no reason why cadres as represented by corporate boards couldn't ensure meritocratic nepotism - the selection of the best from a pool of those loyal to 'the cause' of the mega in question. It may be that Civire are found in more labour oriented or military careers due to the PF supported concept of borderline ancestor worship among the Caldari, in a similar way to 'military families' of the modern world - you go into the career of your forefathers because there is social stock or personal pride in doing so. The Civire born to a marine who goes on to become a bank clerk has less to gain from his parentage/familial reputation than the same Civire who goes on to the officers corps, pushed to succeed but given leeway due to 'a good family name'.
The above is a very simplistic and broad description of how I feel things work, due to the staggering size of the State, but we also have another key element of the Deteis - tube children. Custom 'grown' children raised in State creches for a variety of tasks. For those of you into 40k lore this all feels a bit Schola Progenium (as State creches also house orphans afaik) and a great way to indoctrinate individuals in corporate and State culture. The high number of Deteis functionaries may then be explained by simple genetics - they have been bred from the gene-stock of the best and brightest (there may even be some law in place that individuals at a given GPA/achievement level must donate gametes to the tube program).
Nature not being the end of the argument, this tube/orphan program will likely have to be significantly funded to ensure the highly militarised, tube-program endorsing State raised children ready for the employment demands of tomorrow. So here you have a program that is only applied to the Deteis in large enough numbers to provide capsuleer viable specimens over time, entering them from artificial womb to end of education into a system that is identified as 'of value to the State'. In a way, Gotti, I feel that this is the biggest element that backs up your assertions of Meritocratic subversion, on a scale that would be industrial and horrifying IRL.
Even with nepotism out of the picture as a tool of control for anything but the upper echelons, entire generations are raised from a sterile, state-sponsored cradle to a likely ignominious, state-funded grave (vat) - all the while praising the State for 'giving them everything they have' - a truth that is reinforcement to patriots and nationals and likely a sickening corruption of the natural order to serve the corporate machine to outsiders.