I put my 6* DC/DR as my right side FK taker last game as i wanted all of my starters to have a goal. He got a goal and an assist and his first MoM. If your regular taker is struggling, try rotating other players that might not get much of a chance to score. Most of my players bought in previous seasons have fairly balanced stats compared to the new nordgens so I wouldn't do this with new defensive player buys.
I don't put my STs taking FKs as I want them to be in the box looking to connect with headers or rebounds. Unless they are either footed with FK SA. But it's been 5 seasons since I had a good one of those.
Usually, I just put the player with the highest aggregate rating of shooting crossing and finishing.
Or I switch it in game to whomever is rating well, gotta make those gut decisions.