They are nothing but direct stock manipulation that was 'legalized' at the same time where executive compensation was moved from salary to... stock, so that you end up with a quasi-legal (stock manipulation by executives is supposed to be illegal) corrupt incentives system.
Two things:
-Stock buybacks are not manipulation, they’re simply a way to return cash to shareholders and then the shareholder decides when to incur tax liability. A company is well within its rights to issue additional shares or buy back and destroy shares at their discretion. It’s functionally equivalent to a dividend without a taxable event.
-Corporate boards award stock grants to executives because they want management to be aligned with shareholders. I think executive compensation is excessive, but stock grants do align management and shareholders.