STEEM inflation is reduced every year by 0,5%. I think it's around ~8,5% today.
I know we have some extra inflation atm because of the recent insane price swings and an excess of SBD that can now be converted to STEEM but that will stop very soon.
From now on it should take at least +10 years or more to double the total supply of STEEM.
I'm sure we can double the total value of our blockchain in the next 10 years with ease to offset this.
There is no worry long-term. I personally add all that inflation talk to the FUD pile.