I'm not sure why the writer thinks a man of Darcy's background (a wealthy, independent heir, the grandson of an earl) being a shy man covering his discomfort with a veneer of arrogance is more realistic than his actually being arrogant.

The problem with discussing this, however, is that part of the answer is likely to be in chapters we can't discuss yet, as Karen 2L pointed out. We don't get to see the process of Darcy's change, but we might get to "hear" his explanation of it.

However, I think that part of the answer to your question about the Times reviewer's interpretation is in Chapter 4, which we certainly can discuss. The narrator -- not Lizzy, not Mrs. Bennet, not the locals, but the narrator -- tells us that Darcy is haughty. She doesn't say he appears haughty, or that he uses haughtiness to cover shyness. She says he is haughty.

How can that be squared with a "shy, awkward suitor whose seeming arrogance camouflages insecurity and deep sensitivity"?