There's a single reason why American is the least attractive of US legacy carriers (in terms of investing, anyway): its balance sheet.
If most airlines and certainly those in the US are loaded up to the hilt with debt, American goes so far as to boost negative equity - any startup would go belly-up with a balance sheet such as this one.
Now, you can survive and even generate decent returns with a precarious capital structure, but of course you're super sensitive to any shock on the demand side of your business, hitting both revenues and margins - and that is where the clouds gather on American.
After the industry's recent warnings re falling travel demand, the already cut-throat competition for market share will get yet more intensive, while margins will inevitably come under pressure.
I fail to see why American might be an attractive investment proposition outside of the rosiest of economic outlooks, which is not what's at hand right now.
How well do narratives help inform your perspective?