Posey is probably the ceiling, but like I said, the total career really doesn't matter in so far as whether the pick is considered a success. Do the Mariners care how successful A-Rod was for the Rangers and Yankees? Does it affect the Orioles view of how the Machado pick turned out if he bombs for the Padres?
With Posey's service time games, he was actually under club control through 2016, his age 29 season. He was worth 34.3 rWAR over his club controlled time and has had his two worst seasons by WAR in the two seasons since.
Posey was actually more valuable by rWAR than Machado (33.8) over his club controlled period, despite playing catcher and being in a league without the DH that could have given him more at-bats.