There are a few elements to this question. First, the specific issue you're asking about: favoring imports over exports was part of an Ottoman economic strategy which historians call provisionism. That means that the empire's leadership was primarily concerned with ensuring that prices for basic goods remained low, particularly for the citizens of Istanbul, where political unrest could seriously threaten the government. This is in contrast with European mercantilism, which pushed governments to maximize wealth generated through trade. The Ottomans of the 16th-18th centuries weren't interested in achieving a profitable trade balance with Europe, they were interested first and foremost in keeping their population satisfied. This meant banning the export of grain, a policy first enacted in 1555 in response to the empire's rapidly rising population, which was causing shortages within the empire. This didn't stop all grain exports, but it's an indication of what the Ottomans saw as ideal and attempted to implement. Export of goods other than grain, however, were not banned as your quote from Kennedy seems to imply. The Ottomans maintained a lively export trade to Europe, which grew in volume particularly during the 18th and 19th centuries. Among these some of the most significant were raw materials used in textile manufacture, such as cotton and silk.

On this, see McGowan, Bruce. Economic Life in Ottoman Europe: Taxation, Trade, and the Struggle for Land, 1600-1800. Cambridge: Cambridge University Press, 1981.

Ottoman provisionism was less conducive to the development of capitalism, but I think describing it as "primitive" is misleading. It was simply a different type of trade strategy which was based on different assumptions and goals. It's not so much an issue of European "superiority" but of Ottoman "difference".

 

Now, when it comes to Kennedy more generally and the issue of "decline":

Ottoman history has changed quite a bit in the past few decades, as historians have reexamined a number of our fundamental assumptions about how the Ottoman Empire functioned in the light of both new evidence and new methods of reading old evidence. The result of this has been a revolution in the field, as historians have abandoned the concept of "decline" almost entirely. A lot of stereotypes about the course of Ottoman history from the 17th century onward have not held up under closer scrutiny, thus historians nowadays are much more inclined to emphasize the empire's continued strengths rather than its weaknesses during this period. For instance, the notion that the empire became more inward-looking and conservative seems to fall apart in the face of increasing economic and diplomatic interaction with Europe during the eighteenth century.

However, these new developments in Ottoman history have been slow to spread outside of the field. Kennedy, as a historian of Europe, would not have been familiar with the new work being done by Ottomanists and likely relied on older texts. Ottomanist historians have long expressed frustration with Europeanists who repeat what are now considered to be outdated interpretations. Take this quote from Ehud Toledano:

In the scholarly literature produced by Ottomanists since the mid-1970s, the hitherto prevailing view of Ottoman decline has been effectively debunked. However, only too often, the results of painstaking research and innovative revisions offered in that literature have not yet percolated down to scholars working outside Ottoman studies. Historians in adjacent fields have tended to rely on earlier classics and later uninformed surveys which perpetuate older, now deconstructed, views.

Ehud Toledano. "The Arabic-speaking world in the Ottoman period: A socio-political analysis". In Woodhead, Christine. The Ottoman World. Routledge, 2011. p. 457.

In other words, be skeptical of what you read about the Ottomans in works written by specialists in a different field, especially if those works are themselves very old, as is Kennedy's (1987). Look at what books they cite - if they're citing their information on the Ottomans to books written before 1980 at the very earliest, it may be best to disregard what they say.