I'm really not on this boat of "significantly different defining mechanic"...nor have a horse in this race as I do not play in Eberron and/or use an artificer in my games...[nor, apparently, a problem with mixing metaphors]. I mean, what is a Warlock's Invocation if not just "Channel Divine" with a refluff? What do they do? Oh, arcane magical effects...SO it's like Channeling the Arcane? No. They're invocations. So they're spells, then? No no! They're invocaaationnns. Warlocks only, man! Ah boogedy boogedy boo!
There are, what 47 out of 50 class/subclasses [hyperbolic but not by much] that have spell use? What's the significantly defining feature there? Oh look! Different spell list. Really major defining there. Martial types are getting some combat something and Extra Attack. Barbarian:"Reckless Attack" at 2nd, Extra Attack at 5th. Fighter: "Action Surge" @ 2nd, Extra Attack @ 5th. Ranger & Paladin both: Fighting Style @ 2nd, Extra Attack @ 5th.
Basically, everyone is getting some minorly different mechanic with a refluffing and new name as their features...with, then, one "thing that is theirs" that other classes don't get...Be that something major, like Rage or Sorcery Points or Domain spells, or something minorly different and flavorful (but nowhere else) like Invocations, Bardic Inspiration or Paladin Oath Channels ...and then, in the vastly overwhelming majority, an individualized class spell list on top of all of that.
So, here's what I'm thinking...really quickly and trying to follow the PHB format...
[all titles, names and abilities are subject to change for coolness, preference, and/or to protect the innocent.]
INFUSENATOR
You infuse stuff with magic. Blah blah yada yada fluffy bits. [digression note to self for future adventure: mad uber witch named "Blahblah Yada". Moving on...]
Arcane Tinker: You have an innate knack for harnessing and weaving magical energies into mundane items and objects, moreso than other spellcasting/item-crafter folks. Blah blah yada yada fluffy bits.
Arts and Crafts: You are especially crafty, cunning, and can come up with ideas and plans given what seems to others completely hopeless situations. Blah blah yada yada fluffy bits.
That looks like my Tinker class. But instead of dice, you get Genius points. You spend points to create, recharge, or maintain a gadget. Some gadgets use more than one point.
And no spellcasting outside of subclass.
"But Minigiant, why won't parties leave the tinker home where it is safe?"
Because the tinker uses their gadgets better than anyone else. While a tinker can make a flameslinger that casts
burning hands for 2 Genius points, only the tinker can understand the fuel gauges to cast it as a 2nd level or higher spell. Or his repeating crossbow crits on a 18-20 in his hands.
Gadgets:
FiLAMESLINGER (Magic)
Base cost: 2 Genius Points. 100gp of materials.
Base charges: 2 plus 2 for every addition Genius Point
This is a two handed gadget. The weilder can use an action to spend a charge to cast
burning hands as a 1st level spell.
Tinker only- A tinker can use more than one charge to cast
burning hands as a 2nd level or higher spell.
REPEATING CROSSBOW (Gnomish)
Base cost: 1 Genius Points. a heavy crossbow, 10gp of materials.
Base charges: None
This crossbow loses the loading property and gains reload 5.
Tinker only- A tinker scores a critical hit with this crossbow on a roll of 18, 19, or 20.
PISTOL (Renaissance)
Base cost: 5 Genius Points, 250gp of materials.
Base charges: None
This gadget is a pistol (MM)
Tinker only- A tinker scores a critical hit with this pistol on a roll of 19, or 20.
SPRING BOOTS (Gnomish)
Base cost: 1 Genius Points. 10gp of materials.
Base charges: 5 points
These pair of shoes. Their wearer can use a bonus action to spend a charge and increase the wearers long jump distance by 10 ft and their high jump distance by 5 ft until the end of their next turn.
Tinker only- You can spend 2 charges and increase the wearers long jump distance by 30 ft and your high jump distance by 15 ft until the end of your next turn.