+1 for stuck or sticky bobbins on the discs. You only need one to have seized on an individual disc to through things out and create a juddering problem. The effects can be magnified further if the calipers, pins, piston etc are sticky and corroded too. If the bobbins are stuck through corrosion, then the moving parts of the caliper are likely to be in the same or similar condition. All this is not unusual on a bike used through a wet winter.

I very much doubt that all three discs have warped.

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