I can only answer as far as England is concerned, but in that specific case: very much so, yes! Master cooks were a very senior and important position that required the position-holder to supervise a large number of staff, not just in the kitchen, but in other food related workplaces on the estate such as the pantry and the brewery. A noble's master cook would be expected to oversee the cooking of meals for his boss even when they went to visit elsewhere, so if you were wealthy and important, you definitely wanted to make sure you had a good one. The best of these master cooks were highly sought after and commanded considerable wages, and were frequent recipients of gifts and traditional privileges to portions of certain goods that were purchased or produced on site.

In general, there wasn't much hiding of recipes per se. The idea of a formal recipe was a bit alien to the food culture of the middle ages, a given dish would rely on a set of orally and practically learned principles that a cook had mastered (or not, plenty of cooks were terrible, obviously) in their career. A number of master cooks wrote their recipes down... in a sense, but these weren't really instructions on how to cook things (as you'll see if you ever try to make any of them) so much as a general guide to ingredients and preparations, as part of the master cook's negotiations with the stewards and clerks that were responsible in large part for the estate's purchasing (though master cooks did some buying as well).

That said, there certainly was a degree of obfuscation to the way professional cookery functioned. And part of that was accomplished through guilds. Like all guilds, guilds of cooks guarded the secrets of their trade, kept out outsiders, trained apprentices and controlled prices. But the status of most guild trained master cooks was relatively humble (they were actually rather poorly regarded, generally), running modest urban cook shops and the like. (interestingly, women were often part of cooks guilds, but there are no records of them as master cooks in noble households). They did not have anything resembling the status of their fellows in noble kitchens. And indeed, although a formal guild apprenticeship offered one potential route to that kind of level of cookery, many simply learned on the job in large kitchens. Travelling to foreign countries and learning a wide variety of exotic cuisines was also a pretty strong career move for the aspirational chef, in England chefs who had trained in France, Spain and elsewhere were highly regarded. It's kind of how top kitchens work today. It's difficult for any given technique or dish to remain absolutely proprietary because kitchens cross-pollinate so heavily, and draw inspiration from each other. So yes, a professional cook's secrets were probably not something the average person could necessarily access, but what a noble retained a cook for went beyond simply the recipes they knew, to their level of skill, which is something that doesn't really need to be kept secret in the same way.