Huh, that's weird logic right there. You should be careful not to assume things I didn't say.
Koulibaly is in no way a stop gap signing, he is a signing to immediately make the team better right now and the future.
Never said we should gift youth chances, but the fact is having an older CB of high quality means eventually the youth CB will have more chances to break through than if we right now had like 4 young starting-quality CBs.
If we sign him, and over the next 5 years some of these youth CBs show there stuff in the few games they get chances then great, if they don't show the quality then bin them. I'm banking on the odds that one of those 4 become quality for us, considering how quick Eric got into the team.