Steve
Mostly Harmless
I suspect you're right and I'm glad you said it.Speaking as an outsider, I suspect that it's a bit of each.
1) Some Aikido practitioners train as a spiritual path and/or a cultural art. For those people the length of time necessary to become reliably combatively proficient is beside the point.
2) Aikido's strengths as a martial art are (IMO) focused on certain niche areas of application. If you are trying to force it outside of those areas it is not going to be so reliable.
3) I really do suspect there is something to the idea of Aikido as a graduate level art for people who already have solid combative skills. As I mentioned earlier, I can look at high-level Aikido practitioners and see useful stuff I might be able to learn from them - but I have 34 years of a fairly well rounded martial arts career under my belt.
Another thought related to #3. Ueshiba spent a lot of years as a rough-and-tumble martial artist who fought challenge matches and worked as a mercenary before he moved into his "peace and harmony with the universe" phase. Many Aikido practitioners may be trying to practice what he taught in those later years - but I suspect it may not work so well (combatively) for those who don't have the prior combative background that Ueshiba had.
That's speculation from an outsider, though. I'd be curious what Spinedoc thinks of my theorizing.