True, and as long as practically the majority of exchanges between cryptos go through BTC or ETH, and the same two are used for transfers to and from fiat, bitcoin blockchain's speed and fees are very important.
As for Steem, it would be very nice to be supported by more exchanges (for now we have +1 with Binance and -1 with Poloniex). Other than that, Steem on! :)
I’m curious did Poloniex decide to stop listing STEEM?
No, there's a warning displayed since 'forever' on the STEEM/BTC pair, saying STEEM deposits and withdrawals are disabled until a solution is found to whatever problem there is (I'm not really sure there is one).