I would argue that in today's game the attacking runs of fullbacks are arguably the most crucial on the pitch, as they have the most time and space than anyone else.
I understand where you are coming from but we have holding midfielders for a reason, if at any time we are presented with a challenging winger to deal with our fullback and midfielder simply need to work together to close down the opposition effectively.
Some would argue Kolarov is not the greatest defender, and that may be the case but I can recall several times this season he has come up with a great block or goal-line save at important moments. Hopefully the team can train well this off-season and learn how we can utilize Kolarov's power to our benefit, instead of what looks like more aimless hard low crosses into the box. I'll take his thunderbolt shot any day of the week though, that could be the difference in a tight match and if we have a player capable of producing magic at the fullback position we should stick with him.