Size is a definite difference between the Flames and the Oilers. I really do think that small players can definitely turn into impact players, but too many of them on a team becomes an issue. Some of the Oilers top ranked prospects over their rebuild have been:
Gagner - 5'11"
Cogliano - 5'10"
Brule - 5'10"
Eberle - 5'11"
Omark - 5'10"
Yakupov - 5'10"
Nilsson - 5'10"
That is a lot of players under 6 foot. Taylor Hall and RNH are exactly 6'0" btw.
Contrast that with the Flames:
Gaudreau - 5'8? 5'9"?
Baertschi - 5'11
Klimchuk - 5'11"
Granlund - 5'11"
(I don't think I missed anyone else, have I?)
The rest of the Flames more talented prospects at the forward position are all above 6 feet - Jankowski at 6'3, Monahan at 6'2", Knight at 6'2", Backlund at 6'0", Reinhart at 6'1", Poirier at 6'1", Arnold 6'0" (and built like a brick), etc.
There is good reason why many people think Gaudreau will not become an every day NHL player (though I personally think he will) - and that is because of his size. The Oilers put together a core that was very small - Hall being the only body with size. The Flames look to be putting together a core with size. Oilers had other prospects of size as well - Hartikainen, Vande Velde, and a couple of others - but I am not sure I would really consider them part of the core. Either way, they didn't go on to become impact players. Listing Ferland would be equal I would think to Hartikainen AT THE TIME, and the odds are against either of them being impact players in the NHL. I really just comparing the 'top 6' or what should be the 'core' in terms of size.
Also, where do most people think that the Oilers and the Flames compare? Was drafting Monahan this season equal to the "Hall" year, or was this equal to the Gagner year? I see it as more of the Gagner year, and in which case I STRONGLY feel the Flames are 'ahead' in their rebuild if that is indeed the case. If not, Oilers were ahead at the top end (Hall, Paajarvi, Eberle, Gagner), though the Flames definitely have more depth at this time than the Oilers.
I think any way you slice it, it is difficult to prove one way or another without time. I think this will be one of those threads that will be re-visited years later. Without more Flames prospects actually making the NHL and contributing, there is really no way to 'prove' that the Flames are better at drafting, and thus 'ahead' of the Oilers at the same point in time.
My bet is that the Flames are not as terrible as the Oilers at drafting. The Oilers had way too many misses in the years leading up to their rebuild, and during the rebuild itself. This is why they Oilers are still under-performing.
Size is not everything. However, I can't think of any team in the NHL that has a top 6 that average under 6', and who are successful. Montreal did so for a short time, but are trying to get bigger themselves.
I don't really know what this 'proves', but there is probably at least a slightly larger probability having prospects with size (and who still have skating ability and skill - not just 'big clumsy oafs').
I was a bit concerned after the 2011 draft watching Feaster draft Baertschi, Granlund and Gaudreau. However, he has supplemented that nicely with Janowski, Monahan and Poirier at the higher-end of the subsequent drafts. Oilers just drafted too many small guys throughout their rebuild that slot in their top 6. The 'boom-bust' types.
Maybe the comparison is still rather meaningless, as many prospects that 'should' become NHL players seemingly never make it, while others that are considered long-shots end up being impact players. I guess the next few years will show if indeed the Flames are in a better position now than the Oilers were at the start of their respective rebuilds.
EDIT: All sizes were from
http://www.eliteprospects.com. I don't think I missed any of the Oilers top forward prospects. I wasn't as familiar with them as I am with the Flames'. Feel free to correct me if I am wrong.