This is a common misinterpretation of the labor theory of value. I understand it like this:
I am a capitalist and my money goes to pay labor to create a thing that I sell in a market. The workers create thing in the production process. I have captured a portion of the labor's true value based on the market, bringing me profit - what Marx called "surplus value."
I turn around and reinvest that profit into another business that brings me more profit. Rinse and repeat, forever.
But that profit is nothing but a portion of the labor's true value as reflected in the market price, and therefore the labor created the value. The market did not create the value. The market decided on a price to pay for the value created by the labor.
Much like "machines all the way down", value is labor all the way down.
It's not tautological because it assumes that __management contributes nothing.__ Management's decisions about what to build in, how to build it, etc... are worth __nothing__ to Marxists.
Related: when Marxism was actually implemented, they had big problems with not building the right things, and building the things they did build poorly. For example a factory was assigned the task of building N pounds of nails a day, so they just built one giant nail that weighed N pounds (and was totally useless) rather than buliding what was needed. Because it turns out, management is actually needed and useful.
[And so are price signals, but let's take baby steps here!]
The Marxist view is that capitalism is inherently exploitive. You said it yourself: the capitalists are "captur[ing] a portion of the labor's true value." That isn't something you say about someone who is doing an essential part of the work.
In the Marxist view, the work just inherently "happens" (like water flowing down a stream) and capitalists can only be like a water wheel "capturing the value" that's flowing past. Of course, this is bullshit, but that is the mentality.
I am a capitalist and my money goes to pay labor to create a thing that I sell in a market. The workers create thing in the production process. I have captured a portion of the labor's true value based on the market, bringing me profit - what Marx called "surplus value."
I turn around and reinvest that profit into another business that brings me more profit. Rinse and repeat, forever.
But that profit is nothing but a portion of the labor's true value as reflected in the market price, and therefore the labor created the value. The market did not create the value. The market decided on a price to pay for the value created by the labor.
Much like "machines all the way down", value is labor all the way down.