Listen, streamlined and organic games can appeal to everyone. Someone could pick up Civ5 and master the fundamentals it inside a week, because it's so streamlined. That's what streamlining is: taking away the unnecessary clutter that would confuse and alienate your new target audience - Civ Rev fans who wanted something a little more robust, but not too difficult.
You do have a point, though - is Civ5 streamlined enough? Maybe there's room for more streamlining; that would help it more quickly appeal to players who enjoyed Civ Rev but aren't quite ready for the complexity of a challenging strategy game. Future patches could potentially help, especially by spicing up the early game with some more engaging content, as you noted. Plus, there would be financial benefits to to adding (or removing) features that would attract more of those players and retain a newer, more casual audience with the Civ5 franchise. It's important for Firaxis to expand their profit margins on this product line, and it looks like Civ5 is a step in the right direction in targeting that untapped market segment.
Unless they want to finish civ series with ciV. A lot of people preordered ciV. Why? Because it's civ. Now how many people do you think will preorder if they announce right now that Firaxis accepts preorder for civ 6, with lead designer Jon Shafer?
Sure, streamlined and civ became easier. But will people still be FANATIC to a game that is easy to master and now mediocre? Civ 5 is not a bad game, but there are too many good games around as well. Don't forget that other computer games than civ. If there were no competitors, then civ 5 made a right decision, but the assumption is obviously false.
What is surprising is that when they say it's hard to come up with something better than BtS, how about thinking,
is there civ-like game that makes more money than civ?
It is contradictory. No one forces Firaxis to make only civs. If they really throught civ was too complicated for many potential gamers, then they could also expect that the title of civilization could keep away people from ciV. Instead, they could start a new series, say Sid Meier Bros 1.
But they didn't. They made screenshots that looked like it's refined version of cIV. They've never spoken of streamlining. And they gave the title of civilization V, because they know CIV DOES ALREADY HAVE LARGE AUDIENCE AND NO CIV-LIKE GAME DOES BETTER!!!!!
It will get better? Certainly patches won't do it. An expansion pack or two? And how long will that take? A year or two? And think of that other causal gamers who would try and go away from ciV in the meantime and say "I tried civ series, and it was a mediocre causal game just like everything else. That civ fanatics must be pathetic fanboys." How could one keep that gamers to civ? Not only Firaxis can make great stuff.
It is hard to earn trust, and it gets away easily in no time.