He didn't, though. He advocated improving healthcare, but not to the extent that Warren does. And he castigated the banking industry but never proposed anything at the level Warren is proposing.

Besides, this isn't even the question. The OP said that Warren is a middle of the road Democrat. Compared to the positions held by the average Democrat Senator/Congressperson she isn't at all. Whether she'd follow through on those promises when elected is a valid question (though much like Obama, it wouldn't be under her sole control), but that doesn't mean she isn't left-leaning.

To what extent does Warren advocate improving healthcare? She went from "medicarefor all" to "actually medicare is just a framework" in just a month. On her platform page she seems to have abandoned single-payer entirely.

How can you trust a candidate who changes platform from progressive to milquetoast centrist so quickly? How can you trust a candidate who said several months ago that she wants to eliminate billionaires, and yet who continues to get major contributions from at least twenty billionaires?

I find it very hard to believe that Warren is genuinely left-leaning. Based on her behavior, it seems to me much more like she is a centrist candidate wrapping centrist ideas in left rhetoric.

You probably haven't met Warren. She's a force of nature. She's data driven, and extremely tenacious.