If your baseline is a broken paladin everything else sucks.
Yeah, it's this. The class doesn't suck, and you don't have to wait until level 10+ for it to start getting good. Unlike most other classes, artificers are not overloaded at the beginning levels and not underloaded at later levels. They have a nice amount of good and worthwhile features at low levels (Infuse Items, Spellcasting with cantrips, Subclass Spell Lists, great subclass features, Flash of Genius, etc), but also get a ton of great features in later levels (10 free castings of cure wounds/flaming sphere? Yes please! Attunement to 6 items? That's amazing! +1 to all saving throws for each item you're attuned to? Even better!).
They're not super front-loaded. Paladins are. They get Lay on Hands, Spellcasting, Divine Smite, Channel Divinity, Oath Spells, a Fighting Style, Heavy Armor and Martial Weapons proficiency, Extra Attack, Aura of Protection, and so on all at fairly early levels. They get so much from the base class that the subclasses barely give them anything and they have to be MAD (STR/DEX, CON, and CHA) to balance them out.
Artificers are different. They only get up to Medium Armor and Shields with only Simple Weapons (and maybe firearms) for their proficiencies. They get Magical Tinkering, which is mostly a roleplay feature, Spellcasting with Cantrips, which is good but not super amazing, they get Right Tool for the Job, which is super useful in the right circumstance but nowhere as good as Channel Divinity, and they get Infuse Item, which is awesome and amazing, but very limited and restrictive. This allows for them to be very SAD without making them being OP.
Their lack of outright AMAZING main class features moves most of their defining aspects to their subclass. They get most of their subclass features earlier on than a Paladin does, and they get more features from their subclass in general than a paladin does. Just look at how many class features an Armorer or Battle Smith gets at just level 3. They have to get a lot of things from their subclass in order to not suck. (Battle Smiths get Int-based Hex Warrior, Martial Weapons, Extra Spells, Smith's Tools, and an animal companion better than the PHB's Beast Master. Armorers get Heavy Armor proficiency, buffs to any Armor they're wearing, two different combat modes for the armor that let them be a brawling tank or skirmishing sniper using their INT for everything, Extra Spells, and Smiths Tools.)
tl;dr: Artificers are SAD to balance themselves out and much less front-loaded in main class features than a paladin is, but much more front-loaded in subclass features than a Paladin. Paladins are MAD to make them not OP, have to expend their main resources to be the best Nova they can be (which is another balancing factor), and have to be a lot less versatile than an Artificer in order to now be OP.
@Zardnaar, The problem you have with the Artificer class isn't a problem with the Artificer class. The problem is you letting your Paladin be as SAD as the Artificer. Cha-based Shillelagh is something only attainable through multiclassing into a Tomepact Warlock, but you let them get it as a racial feature. Additionally, you haven't been super strict about keeping track of spell slots, which will definitely make the Artificer feel weaker than the Paladin.