I would assume most exchanges need inventory with which to make a market on their exchange... I can't say for certain but I would assume to make that market they would have to purchase coins if they don't already have the inventory. Which means getting on big exchanges is both a short term positive for prices and a longer term positive as it provides yet another gateway.
Though I do get your point that we need to actually create some fundamental value here if steem is to survive long term.
I think we need to focus more on fundamental value if steem is to survive even short term. There will come a point where the price falls too low and we will enter a death spiral.
Big exchanges don't really need to buy too too much because their userbase will transfer enough over that they can work with. (we all know most are running fractional reserves anyway)
Do we know that though? And how can we know that?
Aside from that though, they will still need that initial inventory to get enough of an order book set up to show a fairly liquid coin.
Do we know that exchanges run fractional reserves? It's happened enough times in the past that I'm pretty confident it is the norm.
Maybe they do need to have inventory to set up an order book, but ... that doesn't really build value for steem, at least not for any significant portion of time. We've been here long enough to see steem get on a good many exchanges. The price continues to decline. Exchanges are not the answer.
Certainly not the whole answer, but they are part of it. Especially with exchanges being extremely local in who they serve when we are talking about a global product. There are regions in the world where you cannot buy steem yet you can get on the steemit platform... that shouldn't be.