Manny finished the year with a .304/.370/.580/.950 batting line over 60 games, notching 2.8 rWAR. Would be a 7 WAR season even extrapolated over 150 games. That would be good for his 3rd best year of his career, just behind 2015 (7.5) and 2016 (7.3), years in which he played 162 and 157 games, respectively. If we spread it over 162 games, it would be 7.6, which would be his best of his career.
Obviously, he might not keep up the pace. Alternatively, his pace could have improved. Point is that he had a hell of a year and there's no way the Padres are upset about the deal right now sitting at the end of 2020.