I rotate a lot of different canned/wet foods and have used Royal Canin and Merrick. Honestly, I don't notice much of a difference at all...Toki likes them and does fine on both. She's not very picky! We tend to use Natural Balance Stews, Hill's Ideal Balance, Wellness, TikiDog, Party Animal, Weruva, and Earthborn moist entrees the most...whatever I can find the best deal on locally
Toki is 2 1/2 years now but when I got her at 10 weeks old, she came to us eating just kibble and we only fed her kibble pretty much exclusively the first several months that I had her and she did perfectly fine. Occasionally I'd mix in wet food just because I had it but it was not a regular thing.
If your puppy is doing well with the canned Merrick and you don't mind the cost of feeding it, I'd stick with that. It's not necessary to feed wet food or even a combination of wet/dry although I do believe it is beneficial and try to do so with my pups. I feed Teddy (1 1/2 years) a combination of kibble that I moisten with water and add fresh toppers/canned food and Toki has been eating primarily canned food (we just started experimenting with homecooking) but that is our personal preference.