If the player was that far away they would not get exp or gold from lane or fights as well as being effectively useless as they would be stuck on SKILLSHOT champions varus/jayce/xerth ect Which if they are an average player wouldnt provide much use to their team as they wouldn't be putting out optimal dmg.
the other team once realizing the player is doing nothing but this would just ward and tp flank and kill them.
Or use their 6th member to make team fights 5 v 6
It just wouldn't work. There are alot of other things that go in this as well.
Playing in front of a crowed. No practice with the team. The LAN ping difference 10 ping is a lot different then 75+ on and on.
The skill level at the competitive level of play is just to high for an average player.