The post doesn’t have anything to do with more STEEM on the system in the slightest.

The rewards pool is set, and based on inflation. There is a set amount of inflation in the pool for each round of voting (the payout window).. whatever posts happen in that time period split the inflation pool, based on what votes (by stakeholders) were allocated to it.

The Burn posts simply take their cut of that pool and send it to the null account, which is essentially taking it out of circulation (burning it) as it can never be sold. So, less STEEM that is in circulation, the more scarce it is and therefore more valuable.

Yes, if no one Is buying STEEM the amount circulating doesn’t matter much.. but supply and demand is a thing, the burn post is simply addressing the supply aspect.

I’m speaking of the Burnpost (doesn’t have anything to do with SBD). I’m not that familiar with the SPD Potato project other than they are attempting to use the STEEM to buy SBD to help the price.. sort of how you are explaining. They are actually using the rewards to purchase SBD, different than the burn post.