I would say yes you are right but there are also some aspects that can't be denied.
As Steemit grows and is adopted more and more its market cap will also naturally grow and Steem will be more valuable hence the daily payouts will be higher. But realistically speaking we can't expect it to grow forever and will hit a cap. Once it hits that cap, with the natural expansion of the user base the rewards will inevitably lower.
Another point to be considered is the user base distribution. Yes there will be some to whom 1 SBD will have more buying power than to others but if you look at the current reality: current user distribution of platforms, population per country (considering the development of the country), internet connection availability, education, society influence etc. I believe the majority of users will not have a big advantage between the USD (which is the parity the SBD is keeping at) and the local currency. Yes, there will be a minority of users for which a post's reward is the equivalent of a month's salary but they will be a minority and it is because of the reasons I mentioned before: these type of users don't have access to all the things the others have so they will have less chances of benefiting from this high conversion rate to local currency.
I hope I'm not wrongfully understood. I strongly want everyone in the world to benefit from the Steemit ecosystem and Steem would end world hunger and other issues if possible. But we also need to be realistic and analyse the facts. The world is not going to change in one day.