It's not meaningless from a concept point of view. It is unreliable from an operations point of view if performed poorly, which most are. It is performed poorly for many reasons: 1) it's hard to gauge how far along you are in a task; 2) we have normal, cognitive biases that sort of skew our perceptions of our progress; 3) we lie in order to hide our dirty laundry or kick the can down the road before we have to deal with it.
When project status rolls around, we usually are moving so quickly getting status updates that it ends up going like: "what % complete are you with task A?" "Oh, about 30%." And then we load the 30% and move on. So those three reasons, and likely there are more, are in play and the 30% is simply meaningless.
With EV, you would still have the same problem if you do not have a reliable, objective, verifiable way of measuring work. If you are able to segment your work in a physical way, that tends to meet the criteria of a solid method of measurement. With physical % complete, you do not have even need to ask for an opinion; you just count. Knowledge work is hard to segment in this way. People work around this by assigning a physical % to portions of a product produced by knowledge work. That's okay but still not a very high reliability.
If you're stuck with a duration % complete, then it comes down to how you ask the question. For example, if task A has a planned duration of 10 days, and you're at day 3, the question you want to ask is, 'how many days do you need to finish the remaining work?' This is not fail proof but gets the worker to look at the task in a different way then if you asked how far along are you? Reliability climbs a little bit but you still have ambiguity in the measurement.
Other solutions have been to have a rule such as: 0-100; 50/50; 25/75, etc. This means your progress is (if using 50/50) 50% complete the day you start and you do not get the other 50% until you finish. So the task remains 50% until that time. This works okay for predicting the finish of the hammock task but you still run blind at the lower levels.