That same force would make it impossible for employees to get ahead, investors to make money, etc.
Profit, surplus for workers, investment return are all dependent on there being some kind of "friction" -- which abounds in the real economy.
For instance you want a "moat" for your business such a patent, trade secrets, being at the center of a two-sided market, etc. The labor union quite literally extracts "dues" from workers to sustain the value it helps get for them. Numerous practical problems, such as agency problems, turn up in employing people and it is really not in your best interest to try too hard at paying people as little as possible.
The original Marxian eschatology (before Lenin and the Bolsheviks) was that capitalism was going to eliminate all the friction, there would be no surplus for workers, no profits for business owners, capitalists would be unable to continue the game even if they wanted to.
https://en.wikipedia.org/wiki/Chris_Harman
would say. Harman wrote a number of great books on the subject and was buried next to Marx in London.
Harman himself would admit, though, the the problem of "the tendency of the rate of profit to decline" isn't completely understood or even established (e.g. the basic 'science of civilization' answer is that 'everything fluctuates'.)
I don't buy the idea of "dead" labor though in that capital investment does wear out. You could get a certain bit of infrastructure with 100 person-years or 10 person-years of effort with more or less bungling and the value is the same. You can't just add up the inputs, at the very least you have to apply a discount rate.
I don't think that changes the thesis, because the problem that capitalist has is that he has to put more capital in over time to be competitive and to scale.
Just like a worker would resent working harder and longer to get paid the same, the capitalist resents having to make larger capital investments to get the same return.