Khris another question to this, how is determined in terms of key contributors which player is contributing in a single season or a single match?

Last season for example, my ST was no contributor at all, scoring 5 goals in the first half of the season. During the season I trained him up with the daily videos to about 160% and in the second half (when he was 140%+) it certainly seems like he contributed more and scored more, therefor my other AMC/ST who is usually the freekick taker was performing worse.
If there are certain contributors set in a squad scenario, how can this happen?