The 10, 18 and 20'th lvl abilities are actually very potent, though. It's one of the few times I've seen high level abilities that are so attractive, I don't WANT to multiclass.
10th level is "The Right Cantrip for the Job", allowing you to change your cantrips out with a short rest, something no other class can do at all. The Artilarist can do this at lvl 6 with his wand, but that's akin to Lore Bards getting extra Magical Secrets at lvl 6 while the rest have to wait until lvl 10. But still, being able to switch out your cantrips is pretty fascinating.
18th level gets you "Spell Storing Item" and oh man, this is a doozy. Pick any 1st or 2nd level spell and, assuming you have a 20 Int (which you do), you or anyone you give the item to can cast that spell 10 times! And every day you can pick a new spell, or just recharge the old one! And the item can be any item you can use as a spellcasting focus, so Infused Items work, effectively giving an enchanged item an additional spell it can cast 10 times a day.
There are so many applications to this, from a set of bracers that can cast Cure Wounds to a Cloak of Protection that can cast Invisibility. A Cloak of Protective Invisibility. And you can switch it up every day.
And lastly, that capstone is pretty beastly. It doubles the number of magical items you can attune to, and grants +1 to all saving throws for every magical item attuned. That's potentially a +6 on all saves, giving you a +12 on Int and Con saves. Have a Paladin in the party and you now have a +18 on Con and Int saves. Say hello to never failing another Con save again. In a High Magic Campaign, this will be amazing, as you can give out your created magic items to your party members, but in a Low magic Campaign, this is even better since you can just MAKE your own magical items to attune to.