As you go up in tax brackets y amount is subtracted at tax time until you get high enough that the entirety of x is reclaimed
You’re describing a means tested welfare program.
“Means testing” is to check the recipients income (their “means”) against a schedule of benefits. Higher income=lower benefit. This is how most existing and historic welfare systems have operated. In what sense is your suggestion an improvement?
Asking to test that is a bad faith argument used by the GOP because it’s literally impossible to do without actually implementing the program.
I am no Republican. The comparison is downright insulting.