I think your info regarding EK's hiring practice is a bit misleading. I can only speak about them as they are the only one I'm familiar with.
EK primarily hires FOs, the DEC thing has only very recently been reinstated and as far as I know, no DECs have been hired yet. Since I joined 3.5 yrs ago they've hired about 1000 pilots, all of them FOs. There's no way that DECs will ever be more than a tiny percentage of the total pilots hired.
So your statement that they have an upgrade policy of sorts is completely incorrect. I've been here 3.5 yrs as I stated and I'm getting my opportunity to upgrade now, and my only prior jet experience was right seat on an RJ in canada.
I can't speak for the others, maybe others who have direct experience can, but I believe if you are hired with any of these as an FO, you will be upgraded to capt at some point, depending on company growth and needs.
And, not to be guilty of thread creep:
I do believe AC is on borrowed time. They barely ever "show" a profit. Makes one wonder where all the money is going when the planes are mostly full. The current labour problems are causing them enormous pr
problems in canada, not to mention lingering bad feelings when its all settled from the workforce.
Another point worth mentioning is that the salary and benefits for an FO are so far above what they are in canada that it really doesn't matter that much how long it takes to upgrade.