If Serpent Sting did Shadow damage and, also, raised the dead, you'd have something of an argument.
The difference is that the Goblin Mortar does fire damage and, also, stuns the target, like Xplodium Charge.
I've already answered that. There is double meaning in the title Brewmaster but, only one in the Tinker. Lore-wise, if you'd find a difference between an Engineer and a Tinker, let us know. Because, currently, they overlap:
"Tinkers (or tinkerers and tinkologists) are engineers mostly represented by gnomes, goblins, and dwarves of the Alliance, Horde and the Venture Company."
Weapon types Explosives, various devices
Skill(s) Engineering
Goblins are known for their mechanical expertise and clever, though sometimes peculiar, inventions, and the Tinker is certainly no exception. With his Claw-Pack/Hammer-Tank combo, the Tinker's ingenuity is undeniable. Though his parts may sometimes fail and the occasional explosion does occur, the spirit and enthusiasm of this Hero are never diminished. There truly is more to the Goblin Tinker than meets the eye!"
"Engineers take advantage of their inventiveness to create an immense (and occasionally random) variety of helpful items. By tinkering ceaselessly, and tolerating malfunctions and misfires, an engineer can make utterly unique objects: sight-enhancing goggles, potent guns, robot pets, mechanical mounts, and even more unusual trinkets. Successful engineers use their inventions to solve problems and make life easier, faster, and better for themselves and their companions."
If the Tinker, also, used martial arts, for example, in addition to the tinkering, then you could say they are different.
Yet, they are viable but, other class "types" aren't?
Enchanting would go more towards the Mage, than a Warlock:
"The elves have long delved into the magical and arcane as evident by their cultural centerpiece, the Sunwell. Thus, they have developed a natural Arcane Affinity as a result of the well's magical presence, making the blood elves naturally skilled with arcane arts such as Enchanting."
Blacksmithing is, also, associated with the Lightforged Draenei and Dark Iron Dwarves (through racials), Which have a connection to Paladinism and Shamanism.
Forge of Light
Lightforged draenei racial
5 min cooldown
2 sec cast
Summon a Forge of Light, enabling Blacksmithing.
Blacksmithing skill increased by 10.
Mass Production
Dark iron dwarf racial
Passive
Increases Blacksmithing skill by 5 and Blacksmithing speed by 25%.
I would associate Herbalism with Shamans and Monks, as well:
"Being great huntsmen and natural wanderers with a certain natural affinity, the tauren developed a deep knowledge of the botanical life of Azeroth, using it in various shamanistic rituals, as well as for medical treatment. Because of this, the tauren are natural herbalists."
Mistweaver
"A healer who mixes traditional herbal medicine with Pandaren martial arts."
Monks should have an easy time with Cooking, not alchemy, as can be seen with the Pandaren racial trait.
Way of the Brew
Instant cast
Allows a cook to create delicious brews up to a maximum skill of 600.
"The Way of the Brew is a style of Pandaren cooking mastered by Bobo Ironpaw. The recipes do not focus on any stat, but allow the creation of several unique alcoholic brews which can increase stats or cause amusing side effects."
[Jade Witch Brew]
[Banquet of the Brew]
[Great Banquet of the Brew]
[Mad Brewer's Breakfast]
[Four Senses Brew]
Rogues should have an easy time with Alchemy, as can be seen with:
Crimson Vial
Level 16 rogue ability
30 Energy
30 sec cooldown
Instant
Drink an alchemical concoction that heals you for 30% of your maximum health over 6 sec.
Iron Stomach
Level 60 Outlaw rogue talent
Passive
Increases the healing you receive from Crimson Vial, healing potions, and healthstones by 30%.
Master Alchemist(3 ranks)
Rogue artifact trait
Increases damage dealt by Deadly Poison and Wound Poison by 5/10/15%.
Agonizing Poison
Increases the effect of Agonizing Poison's damage bonus by 5%.
Inscription should be second nature to Mages:
Ancient History
Nightborne racial
Passive
Inscription skill increased by 15.
You're confusing Vantus Runes with Death Knight Runes, instead of Magical Runes:
"Runestones are large blocks of rock carved with powerful magical runes. The high elves of Quel'Thalas built several runestones along their borders."
Rune of Power
Talent
30 yd range
1.5 sec cast 45 sec recharge
1 Charges
Requires Mage
Places a Rune of Power on the ground for 12 sec which increases your spell damage by 40% while you stand within 8 yds.
Casting Icy Veins will also create a Rune of Power at your location.
https://wow.gamepedia.com/File:Blood...Glenn_Rane.jpg
"A blood elf by Glenn Rane. Notice the magical runes around his left eye."
See? you're more useful suggesting, instead of dismissing.