My understanding is that crafting will be mundane. Even alchemy isn't alchemy, it is just mundane chemistry. The items created will not be infused with any power by the crafter. There will be pots and pans, nails, planks of wood, cooking knives, and combat armor and weapons. The biggest difference in combat will likely be decided between those that have armor and those that do not, and, of course, those that have weapons and those that don't. However, a sword that kills a daemon might be infused with some power if it becomes famous, whether the sword was crafted by a novice or a grandmaster. Tho, the novice sword, itself, might not survive long enough to get the killing strike.
Between two people that have armor, the difference will likely be very slight. Think of two equally skilled knights, one with grandmaster crafted full plate, the other with novice crafted full plate, bashing at each other over and over. The one that has the armor from a grandmaster crafter might take a couple extra bashes before breaking, that's all.
Likewise, for weapons. A grandmaster crafter's broadsword might be a bit more durable than a novice crafter's. A grandmaster likely will be able to make a sword sharper and retain its sharpness longer.
The most aparent difference between a grandmaster and a novice weapon crafter, I think, will be what kind of sword they can make. The grandmaster might be able to make a katana-esque sword, a broadsword, a greataxe, rapiers, etc. While the novice might only be able to make a broadsword. But a slicing weapon (katana) tends to suck against heavy armor while a broadsword has much more bashing accompanied with its ability to slice, so it'd do more damage to heavy armor. But if the enemy has only light armor, then the slicing weapon likely would do much more damage than the broadsword; the broadsword would also do more damage against light armor than heavy armor.
In sum, the biggest difference between crafter skill levels will likely be what they can craft, much less so how good they can craft the same item. In other games, a grandmaster crafter's broadsword is night and day compared to a novice crafter's broadsword. In CoE, it'll be more a shade of grey compared to another shade of grey.
I hope I'm wrong, I'd love to be able to eventually craft alchemical items instead of only mundane acids, poisons, solvents, etc.