Whilst at risk of hikacking this thread...
Vendee, I would absolutely agree there is core role for civvi engineering support. It is clearly cheaper but there is a risk, as you say, of the experience and best practice migrating to the civilian end as that is their sole focus.
But we also must strike a balance between sustaining readiness vs vital core competency, be it flying or fixing aircraft. Is that balance always right? Possibly not but I have seen it done very well, and also quite badly as it is easy to become transfixed by routine. But a 'them and us' approach is not helpful from either side.