Armor of Shadows is not doing much for you since you have medium armor proficiency as artificer. You can do better with Scale, half plate or if you need to sneak a breastplate. Unless you have a 16 dex you can do just as well with a chain shirt.
Or, I could not mess with my ability to stealth, and use armor of shadows. This is why I say that number alone cannot answer questions about how effective things are at the table. If I’m not gonna sneak, sure, but I’m also happy to spend an invocation on not needing armor for thematic reasons.
I think you will be bonus-action starved if you plan on using Curse and Hex regularly. That will cut into your damage substantially. You might actually lose damage using Hex since you give up 2d8 when you cast it and 2d8 every time you move it to a new enemy.
Which is why it is, like most tools, situational in usage. Both are there primarily for fighting big critters.
If you move it once in combat you will have to hit an extra 5 times to make up for that damage.
Since the build would be allowed to use EB and artificer stuff together, hitting more often isn’t really a problem.
I might consider giving up Hex completely and taking another spell. Also keep in mind Hex only has a 90 foot range and H. Curse only has a 30 foot range and neither have an attack roll so they don't combine with sniper. Unless I am missing something you can't use them from 240' unless you close first cast it and then run or teleport back.
You might be forgetting that firing from 240 feet away is not soemthing you can actually do all the time.
I would go with undead warlock over hexblade for a several reasons. From tier 2 on you will generally get more uses of Form of Dread per day than you will hexblade curse and since it is a long rest recharge there is more flexibility in its use. Form of dread always gives you the temp hps and does not rely on you being down hps already. Finally Form of Dread works at extreme long range and if you land it the enemies can't come any closer (as long as they can see you). The Frightened condition is pretty darn good, especially if you land it on enemies that have not closed for combat, and I think this would be more effective for the extreme range build you are looking for.
Honestly I only ever look at Undead Warlock when it comes up in conversation, so good catch. Of course I don’t mind being a little squishier on this build.
In general at character creation, I would go with a Wizard over any Warlock for this build. As far as subclasses, Divination, War Magic and Enchantment are all better IMO, in part because it is SAD. That said if you already have your stats and you have a high charisma Warlock is something to consider.
Yeah Art/War is definitely a rolled stats build.
Enchantment is particularly powerful in situations where the enemy is close and you have your artillery because you have reliable decent bonus action damage and you can use your action to hypnotic gaze to incapacitate him every turn after you wail him with your cannon. Illusion and transmutation are not schools I generally choose, but you might be able to get some mileage out of those too with your cannon and all the thematics about making it look like something else or hiding it behind an illusion or making it fire on something that you make flammable.
Yeah I’ll take a look again at those, but my gut reaction is that they will take too many levels to really do what they’re there to do, compared to Evocation. Illusion is very interesting. Conjuration is as well, tbh. Well, from memory. But artificers are good at concentration saves which is the one big weakness of summoning.
As you know I am a HUGE fan of bladesinger, but I don't particularly like it for this build because that subclass tends to think works best when you really focus on melee, to include abilities, spells and ASIs, without that you get a lot of abilities but they are not as powerful and still use your bonus and/or reaction.
I somewhat agree, though I think the real killer for this build is that Bladesinger’s cool later feature requires the attack action, not spell attacks through your wand. At that point, might as well have taken fighter levels. But increased speed, AC, Concentration, and acrobatics, is
very good for a ranged character in my group’s games. YMMV, obviously.
For example if you are not going into melee do you really want to spend a bonus action on bladesong when you could blast instead?
It’s 2d8 damage. It’s not
that big a deal. Bladesong is a BA once, at the start of combat, sometimes just before. Not a big deal.
I think War Magic is better as a defensive buff for this particular multiclass. I am also not a fan of Evocation here, I think the other schools I mentioned above bring more to this build.
Tbh I don’t like much about War Magic. I’d rather go Abjuration, between the defensive buff PHB Wizard schools. Especially with how good the low level Abjuration are, and the fact I’ve got shield autoprepared because I’m an Artillerist.