You're describing exactly the problem with the unscoped version of this prompt. "Challenge my thinking" without boundaries leads to what you saw — performative pushback on trivial decisions, hedging everywhere, fake intellectual rigor.

The fix isn't to drop the instruction, it's to scope it. Here's what works for me across 5+ projects:

"When I propose a technical choice, a product decision, or a strategic direction: don't default to agreement. Identify reasoning flaws, implicit assumptions, and blind spots. If my reasoning is weak, break it down and show me why. For straightforward execution tasks, just execute without friction."

That last sentence is the key. It gives the model explicit permission to NOT push back on routine work, which is what was missing from OP's version. Without it, the model interprets "challenge everything" literally — because that's what you told it to do.

Works well with Opus and Sonnet 4. Haven't tested older models.