If you want proof that "hard work" isn't necessarily "valuable work," simply start digging holes in your backyard. It is hard work. At the end of the day, though, you'll have constructed nothing of value (unless you appreciate the value of holes).
But, as you see, value is a subjective concept. Communism believes it to be objective. But what's valued in communism is simply the biases of its architects. Resources, then, aren't allocated through an objective pricing system weighing conflicting values, but through waits, favors, loyalties, and fiat. Eventually, the system becomes so corrupted it fails.
We've objectively seen the failure of the communist system across cultures over the last 100 years. By now, there should be no doubt about its inherent ills.
Now you've misunderstood me, I'm not saying that because they've done a lot of hard work that what they say is immediately relevant. I'm saying what they've said is relevant, and they've put in a lot of hard work to get their points across. You can't just handwave because in your ignorance you believe you're right and everyone else is wrong, you have to actually confront what they've said
There are plenty of examples of work not being valuable in capitalism too.
I'd put most obscure financial instruments up as one example.
But on the whole, much of communist ideology and theorizing is far removed from reality and suffers from a lack of understanding about human nature. Socialist description and perspective on society is interesting and can be enlightening, but its prescriptions are bad.
Many scientists and thinkers over the course of history have dedicated their entire lives to theories that are ultimately shown to be fairy-tails. It happens all the time.
This is a frustrating and arrogant thing to say. If you can honestly go through and thoroughly criticize the core collective works of great socialist thinkers like Engels, Marx, Lenin, Bakunin, Kropotkin, Goldman and the uncountable thousands who have poured thousands of hours into tomes which are freely available online to study and understand, then you should do so. I would love to read this! You'd probably become a very famous person! But coming out gung ho and so arrogantly conclude that all these people, and all the hard work they have done in both theory and praxis is kaput without a very strong argument behind you is pointless and childish. It stifles conversation and is the reason discussing economic systems with people who don't understand them is an exercise in futility.