Don't confuse "churning" with "churning speed". Churning Amex carsd once seven years (Amex "lifetime" is really about 7 years) is still churning. Churning Citi cards every 18ish months is still churning.
So I wouldn't say churning is dead, but it might be valid to say churning is getting slowed down.
Plus no one other than (possibly) Chase is yet stopping you from applying for multiple cards that earn the same thing (multiple cards that earn AA miles or TYP points at Citi, multiple cards that earn MR points or Delta miles at Amex, etc.)