What we should have is a first 11 (senior pros) and a second 11 (u23s)
The first eleven has the current best players in it and the second eleven has u23s who can potentially be premier league stars.
During games the three subs should be used to give these u23s game time...remember they are all potential stars so can also positively impact games.
During this time if a first eleven player is sub-par or suspended/injured and an u23 comes in and performs well then he keeps his place
At this stage lets use the example of Holgate/Coleman. Holgate is motm in his last game...thus he keeps his starting spot.
In the u23 league Coleman then starts and Kenny is either played in an alternative position or benched but gets minutes as a sub. When Coleman is sub-par or injured/suspended then Kenny takes his place.
Rinse and repeat
Eventually you 'should' see strong competition for places with the hungry u23s pushing the senior pros and keeping their place on merit.
However under Koeman this is not the case.
During the course of the season if the u23 player has pushed out the senior pro then the senior pro should be sold and another young player promoted to be understudy.
In this case if Holgate took Colemans place for most of the season then Coleman would be sold and Kenny would be understudy to Holgate.
When necessary we can also buy stars from overseas if the 1st team player isnt good enough and the u23 player isnt ready to step up