Are you this dense on purpose? The organization had a lot of pitching success stories in 2021 beyond Ray alone. Almost the entire rotation made successful adjustments under the tutelage of Walker, including Ray who redid his mechanics, Matz who tweaked his sinker release point mid season and went on a tear afterwards, Berrios who initially struggled and tweaked his delivery before an end of season run, and Stripling who completely remade his delivery early in the season and had sustained success before missing time due to injury.
It's not Walker alone who is responsible for the success stories, as the organization prides itself on it's collaborative nature. The analytics department, scouting department, pitching coaches and front office staff all work together in formulating plans on who to target based on potential tweaks to unlock unrealized potential. Despite this Walker is the primary guy working with these pitchers and helping them to make the necessary adjustments in order to allow them to have a chance to succeed. It's really dumb for you to assert that he shouldn't receive any credit whatsoever for the obvious success cases, especially in instances where pitchers had failed to the degree that their previous longtime organizations had completely given up on them. Ray and Matz both had some of the best seasons in their careers after having the worst seasons of their careers the season prior, and Walker and the Jays deserve a lot of credit for helping this to occur.
Semien had a similar offensive performance in 2019 so this wasn't completely out of the norm for him. The Jays made a calculated gamble that the 2019 version of Semien was the guy they would be bringing aboard in 2021 and were handsomely rewarded.