Same experience, here. Very hard to base on facts, because every problem and prompt is an individual use-case and measuring agent reasoning quality is notorious

Same experience, here. Very hard to base on facts, because every problem and prompt is an individual use-case and measuring agent reasoning quality is notoriously difficult anyway. But I spend a lot of time with Claude and my overall "feeling" fully matches your description. Quality has deteriorated, thinking takes longer and results become shallow. Something is off...