1) & 2) Um, AXP did reserve heavily through the cycle (and continues to reserve), cut-off some of their riskiest clients and re-oriented their product mix toward charge cards versus revolving balances (loans). They remained profitable through the crack-up. AXP focuses on a more affluent customer and their business model tries to optimize spend, not credit. It is a unique franchise that, as of yet, no one has been able to effectively replicate. There is a first-mover advantage to the affluent network they have built.
3) They do reserve and they already carry considerable excess capital and liquidity
4)This seems a bit far-fetched
I think the main risks here are 1) governments limiting interchange fees (a key component of AXP's attractive economics) and therefore indirectly limiting a company's ability to offer rewards (a key component of AXP's customer offer) and 2) this business is, over time, dependent on economic growth and therefore macro-crackups.
The company does some pretty innovative things with its data, being one of only two issuer/processors in the industry (Discover is the other). It has consistently generated 20%+ ROEs and returns ~60% of annual earnings to shareholders, retaining the rest for growth.