It is not misleading in the least to say that the 5C was a disappointment. It did not do a particularly good job of living up to its all-but-stated goal of penetrating the lower-income market in the developing world, namely China[0].
As GP said, you would be hard-pressed to find someone either inside Apple or outside who would seriously make the argument that the 5C was anything other than a disappointment.
[0] Nor did it even do a particularly good job of selling to lower-income households in the US (which wasn't even the goal in the first place, but since OP mentioned the US, let's address that). It's hard to say, but inferring from the movements in market share, it seems the 5C ate into 5S sales more than it converted Android or Windows Phone users.