I've got some good thoughts on this. Initially I thought the armorer also was kinda... meh. However, there's a few things that make it shine, some of which may require DM approval - or at least warning your DM ;).
First, to differentiate the temp HP artillerist, the only thing I can say is... it doesn't cost you a spell slot if you have to resummon the turret. Also, frankly, the artillerist is a really powerful subclass.
That out of the way, there's a few neat tricks up your sleeve!
As mentioned earlier, mobile + distract on the melee variant can be neat (with or without BB). Without BB you can potentially give disadvantage to two enemies. With it, you can really lock down one enemy. You can also forgo mobile in favor of boots of the winding path, though its a lot less flexible.
However, I think the melee version is the less interesting option.
Armorer is, to me, all about infiltrator mode. The advantages are:
1) You can be stealthy
2) You are slightly faster
3) You can ignore STR. - and I saved this for last because it's kind of a big deal. The problem with melee-mode is even though you can ignore STR req of armor, you still need str to use your weapon (unlike battlesmith). Infiltrator is dex + int only.
And the Lightning Launcher is one of the only ways to make an attack with no hands, since you can chest mount the thing (someone watched too much Ironman making this subclass). It also does 1d6 more damage on its first hit than a hand crossbow.
That said if your DM agrees that the Repeating Shot lets you use a shield + crossbow you should take Crossbow Expert and a hand crossbow and go for the infamous D&D Crossbow + Shield combo, which will grant you a staggering high AC + seriously beefy damage.
The quick "default" attack round will be 2d6+dex on the first hit with LL, 1d6+dex + 1 on the second and the bonus attack (xbow) for a total of 4d6 + dex*3 + 2 (repeating shot's +1) for a round with full hits. Solid. You can optionally add in sharpshooter if you want too.
Alternatively, you can just have a short sword + shield + LL, making you really able to threaten in both melee and at range. That makes you a lot more flexible than the artillerist when things are in your face. It's a lot less damage but you can put that extra feat to work in a pinch.
Ok so lets build this out. If you want to powergame, you can get the TCE custom lineage for the feat + darkvision to be slightly better, but for now, lets just be a V. Human.
+1 dex +1 int so you have your 16 / 16 in primary stats. Everything else season to taste.
Feats
Lvl 1: Free Human feat for Xbow Xpert.
Level 4: Sharpshooter, because we can. +2 dex if you don't want to be "that player"
Level 8: +2 Dex
Key Infusions (3 at level 8)
Repeating Shot Xbow
Repulsion Shield
<anything you want> - I'd consider Goggles of Night (you're a human afterall) mind sharpener, Spell refueling ring (Likely given to a caster so they can get an extra 3rd level spell), enhanced defense, bag of holding, or even Armor of Tools (Thieves). Just be sure 2 (minimum) are "armor" mods. More on this at the end.
Since you've played artificer before you already know that you get 6 infusions known, so be flexible and swap them out as needed. Repulsion shield won't be needed if you find a +1 shield for instance.
Key Skills
If your party doesn't have a character for traps, thief tool proficiency can actually be your jam and you can fill in. That's why I list Armor of tools above. Not only do you have expertise in this, but with Armor of Tools you could have your dex + int + double prof, making you the biggest tool in the game! ;)
Otherwise, nothing special here, fit it to your flavor.
Spells
IMO since we've focused on DEX instead of INT, avoid spells with saves. Magic Missile can do work if you need guaranteed damage. Absorb Elements, Feather fall, Enlarge, Cure, See Invis, Invis, even things like Purify Food and Drink may be handy. I don't think you need an attack cantrip either, so focus on utility that your party needs.
Ok, so far so good but this sounds pretty basic right? I mean all we've really got going for us is lightning damage that does an extra 1d6 per round on a hit, 5 ft of movement speed, and no-disadvantage in plate armor on stealth rolls. Otherwise we're just a weaker version of a battlesmith. You're absolute right!... and that's because you're starting at level 8.
Also you may be wondering "how come you haven't suggested a fighter dip for the +2 to hit" or a rogue dip for sneak... well...
Level 9 and 10 I think are the turning points for armorer, so I want to look ahead to that and we want to rush it as fast as possible.
Level 9 grants you 2 additional infusions (as long as 2 of them are part of your armor, which they will be). That's HUGE! SO much better than artillerist's 1d8 damage per round. Keep in mind your infusions only get stronger as you level. Something like mind sharpener + haste really makes you significantly more dangerous and you don't have to give up a needed infusion!
Finally, at level 10, the build is reaching its stride. And I really do think this is the problem with the armorer, it's "just ok" until level 10. Level 10 changes everything for the armorer.
The big change at level 10 isn't that you get Magic Item Adept (I mean you do), it's that you get access to the level 10 replicate magic item list and now can infuse SIX items.
Let's just pick a few fun things we can now do. Pick your favorite 3 at level 10. (You learn 2 and can swap 1 out)
Fly
Take 1d10+dex less damage from all ranged attacks
Gain advantage on initiative rolls
+1 AC and +1 Save
At will disguise self
Have advantage on perception checks that rely on sight
So, lets go with the basic: Flight and taking less damage from ranged attacks. A nice combo since the only way to hurt you when flying will be ranged attacks or spells and 1d10+dex is a pretty huge bonus (though it does mean you have to drop your shield, but this also frees up both the repeating shot and shield infusion). Let's give ourselves perception advantage too, so we can spot enemies and pretend we're an eagle or something.
And yes, absolutely the artillerist can do this too. The difference is you're doing it wearing heavy armor with 2 more infusions than they are. With each level you can rotate out another low level infusion for a higher one.
With each level from here you're going to get significantly stronger than the artillerist.
So, all that said, if the game is only level 8 and not going on to level 12-14... well, the armorer is "ok." But I think it has a ton of flavor at level 10+. It can stand on the front line like a fighter but have multiple skills on par with a thief. It has a handful of nice utility spells in and out of combat to fill in some gaps.
And this is just one version. You can easily make a melee version that is all about locking down enemies too, or even using the Ogre Power gauntlets, a hybrid version that can do both. Hitting 2 (or even 3 with haste) enemies and then flying out of reach can really mess up some rolls. Or even taking Dual Wielder you can bonus action smack someone with them too. There's actually quite a bit of nuance to the subclass that makes it substantially different from others, and I like that a lot. You could even take PAM with mobile instead and gauntlet tag someone and move away.
Hope this helps give you some inspiration on what to do!