"The Economist" can be taken as a model of good English. However, although this is well-written, grammatical English, the writer is also trying to be clever and entertain his readers by creative choices of words and phrase.
"Fleet of foot" is clear. It simply means "fast." Here, it means "fast" in the sense of "nimble" or "agile." They can change products quickly to meet changes in the market, and get new products to market quickly.
"Fleet of foot" is old-fashioned language that means "able to run quickly on foot." You'd expect to read it in a context like "The huntress Atalanta was fair to look upon withal, yet wondrous fleet of foot."
"Brand-licentious" is puzzling. "Licentious" normally means "sexually promiscuous." Here, I think the writer is inventing a phrase to mean the opposite of "brand loyalty." I think it means Chinese consumers switch brands easily. A Chinese company can't just keep selling the same old product and counting on consumers to keep buying it because it's a familiar brand.