Purina is one of the companies responsible for nutrition research and their foods are good and adequate
It's a good thing some folks want to feed more than adequate food.
Some reasons your vet would recommend it are
1) It is way better than than the cheap junk many kittens are fed
No, it IS the cheap junk food a lot of kittens and cats are fed.
2) If it's on your vet's shelf, your vet gets a cut of the price
3) As it is your first kitten maybe you would not know where to start.
But with all of the web sites and great info out there these days it's much easier to find the right info. Sites like www.catinfo.org are a great place to start.
4) Research into grain-free diets, raw diets, herbal/veggie/fruit supplements is minimal, and your vet may be one who doesn't believe anything until it is proven in research.
Really? So it's ok to feed obligate carnivours things like herbs, veggies, fruit? What purpose does it serve? Cats can not and will not survive on a veggie diet. There has actually been a lot of research done lately. Vets research unfortunately is greatly skewed by the giant food companies that also are their "teachers" if they choose to take food nutrition while in school. Raw "diets" are exactly what cats survived and thrived on for years before human intervention.
5) There are, in fact, so many brands and varieties out there that your vet hasn't the time to become familiar with them.
A good vet will make themselves familiar with them.
Companies like Petcurean use the research Purina has done to make a food that has all the nutrients your kitten does, and then add in their own features: grain-free, low processing, no artificial preservatives, various holistic herb/fruit/veggie supplements... If you look at the ingredients label on your bag of Now!, you will see a long list of vitamins, minerals, amino acids, etc. that they have added to ensure your kitty gets what she needs. You will also an AAFCO statement, don't feed anything without one on the label.
If you look at the same bag of Purina Cat Chow you will see the same list of vitamins, etc. You will also see lots more - grains (cats don't need), by products , flavour enhancers, etc. But, ironically, that bag of dry food, no matter what kind, should never be on the shelves to begin with. Cats need their fluids with their food, not beside it. As for the AAFCO - that's another different discussion.
I do believe that you have made a good choice for your kitten. But keep in mind, every kitten is an individual, if your kitten is healthy, the food is working.
However, if I were you, I would seriously consider a new vet. As a person who is interested in newer ideas, and a more holistic approach to your kitten's health and nutrition, you would be better matched with a vet who is comfortable with your philosophies. I would also have some concerns that a product-pushing vet might also encourage you to do unnecessary tests or procedures, rather than doing what's best for your kitten and listening to your choices and opinions.