I believe all Grey Warden mages are technically apostates, due to no longer operating under the auspices of the Chantry. And if you question Duncan during the Mage Origin in his room after you drop him off, he flat-out tells you that some Grey Wardens use blood magic (though he's never seen it personally) and the Chantry's being unnecessarily restrictive about the whole thing. If you listen to the rumormongering apprentices, 'Wendell' made it through but was barfing for a week after (the dialogue's a bit vague, but I think that makes the most sense), 'Humbert' volunteered for Tranquility, and an unknown apprentice disappeared last week. As for the other Harrowing-age apprentices, Jowan's going to be made Tranquil against his will, and you just passed your Harrowing with flying colors.
If you take this as approximately representative of the norm (instead of the other option, which is simply presenting the possible options) then that's only 2 out of 5 apprentices making it through. Out of the rest, 1 chooses Tranquility, 1 has Tranquility forced upon him, and 1 dies.
It's AMAZING what you can find if you dig around in the dialogue options.
Also, apparently there were only 7 mages at Ostagar: Wynne, Uldred, 'the Grumpy One ' who's also a senior enchanter, Circle Mage in the Tower of Ishal, and those three in the Magi Encampment doing their super-secret magic ritual. What you see is what you get, in this case. That's why Duncan shows up - to make Greagoir give up more mages. That you end up in a pile of crap and end up being conscripted is just coincidence. Those above are 'most of the senior mages', and Greagoir considers it a sufficient contribution. The Circle isn't huge.