Unfortunately, ZOS isn't providing much information regarding the master writs.
Therefore, it is up to the players to figure out how the drop rate is and how it can be improved.
As i did crafting dailies with all my crafting characters I have now completed around 1k crafting dailies during the last 20 days. I will share my statistics here and some information on the specific crafter (achievement state, research state, etc.)
Please feel free to contribute your own data as it might help in figuring out what the drop rates are and how they can be improved.
Diagram Explanation
I will post 3 diagrams for each character.
The first one shows how many master writs have been collected during the first 20 days.
The second shows the amount of vouchers these master writs were worth.
The third diagram shows how many vouchers have been collected in each category per day over 20 days.
1. Main Crafter
All traits have been researched.
All styles prior homestead have been learned.
All crafting achievements prior homestead have been collected.
Provisioning: Purple Gourmet: 9/31 (mostly low level missing), Purple Distillates: 16/31, Golden Recipes: 4/5
2. Crafter
Traits (Blacksmithing, Woodworking, Clothing): From 53, 31, 55 To 60, 37, 64
Styles: Basic Styles, Ancient Elf, Barbaric, Primal, Daedric, Mercenary, Xivkyn, Skinchanger, Hollowjack, a few assassins league (4)
Achievements General: Most "General" Achievements which aren't bound to a style.
Achievements Alchemy: All prior homestead
Achievements Blacksmithing: Master Blacksmith
Achievements Clothier: Master Clothier
Achievements Enchanting: All prior homestead
Achievements Provisioning: All prior homestead (no gold recipes, only a few purple recipes)
Achievements Woodworking: Master Woodworker
3. Crafter
Traits (Blacksmithing, Woodworking, Clothing): From 51, 30, 49 to 61, 36, 61
Styles: Basic Styles, Ancient Elf, Barbaric, Primal, Daedric, Mercenary, Skinchanger, Hollowjack, a few assassins league (4), Xivkyn partially
Achievements General: Most "General" Achievements which aren't bound to a style.
Achievements Alchemy: All prior homestead
Achievements Blacksmithing: Master Blacksmith
Achievements Clothier: Master Clothier
Achievements Enchanting: All prior homestead
Achievements Provisioning: All prior homestead (no gold recipes, only a few purple recipes)
Achievements Woodworking: Master Woodworker
4. Crafter
Traits (Blacksmithing, Woodworking, Clothing): From 50, 30, 48 to 61, 36, 60
Styles: Basic Styles, Ancient Elf, Barbaric, Primal, Daedric, Mercenary, Skinchanger, Hollowjack, a few assassins league (4), Xivkyn partially
Achievements General: Most "General" Achievements which aren't bound to a style.
Achievements Alchemy: All prior homestead
Achievements Blacksmithing: Master Blacksmith
Achievements Clothier: Master Clothier
Achievements Enchanting: All prior homestead
Achievements Provisioning: All prior homestead (no gold recipes, only a few purple recipes)
Achievements Woodworking: Master Woodworker
5. Crafter
Traits (Blacksmithing, Woodworking, Clothing): From 45, 28, 41 to 56, 35, 52
Styles: Basic Styles, Ancient Elf, Barbaric, Primal, Daedric, Mercenary, Skinchanger, Hollowjack, a few assassins league (4), Xivkyn partially
Achievements General: Most "General" Achievements which aren't bound to a style.
Achievements Alchemy: All prior homestead
Achievements Blacksmithing: Master Blacksmith
Achievements Clothier: Master Clothier
Achievements Enchanting: All prior homestead
Achievements Provisioning: All prior homestead (no gold recipes, only a few purple recipes)
Achievements Woodworking: Master Woodworker
6. Crafter
Traits (Blacksmithing, Woodworking, Clothing): From 46, 28, 46 to 58, 34, 58
Styles: Basic Styles, Ancient Elf, Barbaric, Primal, Daedric, Mercenary, Skinchanger, Hollowjack, a few assassins league (4)
Achievements General: Most "General" Achievements which aren't bound to a style.
Achievements Alchemy: All prior homestead
Achievements Blacksmithing: Master Blacksmith
Achievements Clothier: Master Clothier
Achievements Enchanting: All prior homestead
Achievements Provisioning: All prior homestead (no gold recipes, only a few purple recipes)
Achievements Woodworking: Master Woodworker
7. Crafter
Traits (Blacksmithing, Woodworking, Clothing): From 46, 27, 41 to 58, 34, 53
Styles: Basic Styles, Ancient Elf, Barbaric, Primal, Daedric, Mercenary, Skinchanger, Hollowjack, a few assassins league (4)
Achievements General: Most "General" Achievements which aren't bound to a style.
Achievements Alchemy: All prior homestead
Achievements Blacksmithing: Master Blacksmith
Achievements Clothier: Master Clothier
Achievements Enchanting: All prior homestead
Achievements Provisioning: All prior homestead (no gold recipes, only a few purple recipes)
Achievements Woodworking: Master Woodworker
8. Crafter
Traits (Blacksmithing, Woodworking, Clothing): From 45, 28, 47 to 57, 34, 58
Styles: Basic Styles, Ancient Elf, Barbaric, Primal, Daedric, Mercenary, Skinchanger, Hollowjack, a few assassins league (4), xivkyn (2)
Achievements General: Most "General" Achievements which aren't bound to a style.
Achievements Alchemy: All prior homestead
Achievements Blacksmithing: Master Blacksmith
Achievements Clothier: Master Clothier
Achievements Enchanting: All prior homestead
Achievements Provisioning: All prior homestead (no gold recipes, only a few purple recipes)
Achievements Woodworking: Master Woodworker
9. Crafter
Traits (Blacksmithing, Woodworking, Clothing): From 44, 28, 45 to 56, 35, 57
Styles: Basic Styles, Barbaric, Primal, Mercenary, Skinchanger, Hollowjack, a few assassins league (3)
Achievements General: Most "General" Achievements which aren't bound to a style.
Achievements Alchemy: All prior homestead
Achievements Blacksmithing: Master Blacksmith
Achievements Clothier: Master Clothier
Achievements Enchanting: All prior homestead
Achievements Provisioning: All prior homestead (no gold recipes, only a few purple recipes)
Achievements Woodworking: Master Woodworker
Total