All I am trying to do is get a fair comparison. You can’t compare the AARP card to 10 cards. If you plan on getting ten card in the next six months make one the AARP card. Now we can make a comparison. Nine out of the ten cards are the same so throw them out. What card did we get rid of and replace it with the AARP card? We can now compare the two cards.
Let's say I have $40k to spend, here are the three scenarios:
1. Get two AARP cards, one every six months. Total for the year - $2k.
2. Get 20 mileage cards, minimum return from signup bonuses is $500. Total for the year - $10k+.
3. Get 19 mileage cards, minimum return from signup bonuses is $500. Assuming I spend only $20k on signup bonuses, and have another $20k left, that $20k spent on the AARP card will only net me $400. Total for the year - $10k+, with AARP card capped at $400, which is less than the $500 I got on the other mileage cards.
These are conservative estimates, as I've had many mileage cards net me $1k+ last year.
Even if your argument (cashback > miles) holds true for
spending, it isn't true
overall when you consider a budget and signup bonuses as illustrated above.