He may have looked reckless at times, and given the nature of his attacking role, he was out of position a lot, but he had some of the best stats in the league defensively.
Last season he was 6th highest in the whole PL for tackles which resulted in a turnover of possession - 11 more than Rodri, and nearly double as many as Bernardo, who was the third best at City.
He was 17th in the PL for recovering loose balls, with only Rodri above him at City.
He was 8th in the PL for interceptions, more than double the number Rodri made.
He was 9th in the PL for attempted tackles, and at City only Rodri had a better win % than Cancelo.
I think you’re mistaking or falsely equating making a lot of tackles for being good defensively. They’re not the same thing.
Most of Cancelo’s tackles and defensive actions came in midfield where he was an extra man and could stand off and then jump in when the opposition were outnumbered. It’s a product of the system Pep created where he was an extra man in midfield.
When actually asked to defend as a fullback he was found wanting time after time.