Not messing up is a skill.
Also, split pushing is a good way to counter this.
If the enemy team is all together as 5 and they are winning team fights, you want to divide their numbers so that your team has an even number as in a 4v4, or so that your team has an advantage as in a 4v3. This makes it easier for your team to win a fight, or at least harder for their team to take objectives. Meanwhile you are applying pressure on more than one objective at once, which should help you to make up ground or get ahead.
If you are winning team fights as 5, commit to staying together, even if the enemy is split pushing. You either take/win the 5v4 and then take an objective, or you go as 5 to face the split pusher, and force the bulk of the enemy team to rotate away from the objective they were pressuring.