Mediocre compared to what? Battle Smith is decent at combat. They have Extra Attack and extra damage via pet attack that has it's own turn.
The Steel Defender has 2 + INT bonus + 5 * Artificer level HP and is easy enough to grant Thp thru Heroism and heal thru Mending. It also has a self-repair ability. It's not fragile.
Guidance still helps Artificers over Bards and Rogues until Tool Expertise hits. The Steel Defender even has Expertise in Perception and immunity to Surprise.
The only real issue with the class is a lack of high impact abilities for high impact moments. If a player wants those and can see other classes with such abilities then the grass looks greener, but the consistent benefits of the class haven't lost value.
19 or 21 STR and 19 CON from Infusions helps anyone. Mind Sharpener or Spell-Refueling Ring are useful.
A pass on the spell list is worth considering. A pass on the Infusion list is a good idea, but there are some good Infusions in there.