Using Enchanting was perhaps the wrong profession to demonstrate the higher point. Let me try this again.
Scarcity can be achieved by multiple methods, not simply the length of time it takes to reach a defined end state such as finishing filling three tiered KP wheels. Blizzard’s use of Specialization for DF professions is actually a case in point because the very name ‘Specialization’ is undone by the fact that every crafter can max out their points to craft everything at the highest rank. That is not Specialization by the definition of the word. By actually forcing a Specialization choice on players in their profession(s) Blizzard could achieve the same scarcity. Similarly, the fixed rate of acquisition of Sparks (of all kinds) already creates a limitation that is independent of the limitations from gaining knowledge points or alternative skill bonus(es).
Your point of not making it too fast is well taken, but could be alleviated through the following:
-Player chooses Armorsmith. Learns all armor plans. Filling out the wheel guarantees Armor crafts at R2.
-Player chooses Fine Armor. Filling out the wheel guarantees Belt, Gloves, and Bracers now guaranteed craft at R3 with chance for Inspiration to R4/R5.
-Player chooses Gloves. Filling out the wheel guarantees Gloves craft at R4. Chance to Inspire to R5.
-Adding Profession Equipment and a suitable complementary skill in Hammer Control or redesigned Specialty Smithing now allows guaranteed Gloves craft at R5 with Inspiration now providing other potential benefits. Won’t address those right now but it is an option.
Since a player can choose to truly become a specialized master of one armor piece, or generally improve all crafts but not to the highest quality, they achieve a similar scarcity since only the most obstreperous players would create nine blacksmiths to niche all armor possibilities and another six blacksmiths for weapons and tools.
Edit: Make the gaining of KP or whatever to fill out the specialization take 2-4 months and they’ve preserved scarcity while accelerating capping of profession skill.
Server, play time, and so forth also create huge differences in play experience. The only shoulders I’ve crafted were for my own characters, but I’ve crafted over 100 Primal Molten Gauntlets, mostly through public work orders, even though it is also a Tier slot.
I didn’t say the acquisition rate is balanced around RWF although there is some limitation. But portions of the design philosophy for professions are still based around not providing a crafted alternative to Raid gearing for the RWF. Also, Embellished items, especially crafted with the appropriate missive, were such a huge benefit that the nerf bat swung hard for 10.2 because they said crafted gear was overpowering and out prioritizing compared to raid drops. Even though Blizzard wanted crafting to be another end game pillar, they were willing to subordinate it to raiding when it did not work out the way they expected.
Although I was talking about Profession Specializations (Armorsmith, Dragonscale LW, Spellfire Tailor, etc.), your point about Profession Perks being removed in WoD is also pertinent, and the desire to allow all players to access all crafting outputs in DF. Although it is kind of an oops moment because Primal Extraction is a combat bonus that only Enchanters can get and use even though it is limited to the outside world.
Hopefully this makes more sense than my previous attempt.