Shiel was a more accurate goal kicker in the first 3 years of his career.
Maybe as he moved more into the midfield he increased the power in his kick and took a lot more kicks from outside 50, his accuracy diminished.
We know only too well that kicks often draw or fade at the end of their trajectory. Specialist forwards have learned to use this, for instance Buddy uses a ( natural?) draw that enables him to regularly kick goals from the boundary outside 50, particularly set shots.
Shiel may be able to improve it, but kicking a 60 metre goal at full speed after bursting from a pack and maybe stepping an opponent is always going to be difficult.