Nope, genuine question - why should they have a progression plan when they can buy in better players? That's the way of the game these days. None of the Irish players I mentioned have exactly proven Celtic wrong in their judgement of them. If you're good enough, they'll take notice (or maybe try cash in). If you're not good enough, why should Celtic care? Kenny unfortunately seems to have struggled at Queen's Park, so was hardly about to move up to the Celtic first team.
(Though that said, wiki says four of the current Celtic squad came through the youth team - though obviously that's over quite a while and gives fairly low odds for any given academy player, but for a senior squad it's probably a reasonable return)
We've had a chart on here many times (and
here it is again) before showing a rough evaluation of various European leagues based on Euro results and Celtic/Rangers come out as lower mid-table Premier League sides in it. I think that's quite reasonable.