How much does frequency response flatness actually matter for mixing on headphones under $200?

One thing I keep turning over when looking at monitoring headphones in this price range is how much weight to give measured frequency response flatness versus how experienced mixers describe the same pair after extended use. Manufacturers at this tier often advertise a wide response range, but the shape of that curve, and whether it trends toward a slight low-mid bump or a recessed upper midrange, seems like it could meaningfully affect translation to speakers. Is there a general consensus on whether a flatter measured response correlates reliably with better mix translation at this price point, or do other factors, like driver consistency unit to unit, or the acoustic effect of the ear cup design, tend to dominate the practical experience? I am also curious whether people find that burn-in claims for dynamic drivers in this category hold up to any scrutiny, or whether that tends to be more of a placebo effect that gets reinforced by ear adaptation over time.