Take the most broad and crude measure, educational outcomes, as some, albeit imperfect input to the system and you'll see very unambiguously and consistently that kids with better grades will do better in life, in most measures.
Next time you are at the office, look to your left, look to your right: you will notice conscientious people, probably educated, probably reasonably hard working, team work oriented, and probably bright.
Then hop on the bus and have conversations with the 'average person'. You fill find somewhat less conscientious, less interested, less curious, less intelligent people.
We have very clearly and unambiguously a mostly meritocratic system: as you go from coffee maker, to skilled labourer, to creative worker, to middle management to executive, you'll see a pretty obvious trend.
It's funny how the meritocratic naysayers, probably already in the top 20% of income earnings, probably would believer firmly they are more 'deserving' of their job than the dude who drove them there on the bus, but that somehow, the system 'above them' is 'not meritocratic'.
The issue then becomes one of 'self awareness': we don't like our boss, we are jealous of others who have more, we see some folks 'skip the line' with better access to education i.e. we see flaws or things 'we don't like' to varying degree and so somehow we believe the system is existentially flawed. It's not.
The first time you start to hire people, it becomes perfectly clear: either 'you' are fundamentally part of that of that byzantine, unfair system, inflicting your woes onto everyone with unfair hiring/advancement - or - more likely, you're actually trying to hire decent candidates, capable of doing the work.
So what's more likely: 1) you are the lone hero in an unfair world, trying to hire 'good people' while everyone else is either dumb or plotting like Mr. Bean a fools dystopia - or 2) that most people are like you, trying to hire reasonably good people (hopefully the best you can) and trying to do a reasonable job - and there is some intelligence in that process.
It's the later.
Most modern systems are crudely meritocratic. When they are not, it's obvious, but that doesn't mean those failures are normative or existential to the system.