Why an even split? Why not just go Warlock 2 GOO/7 Stone Sorc? You don't really benefit from an extra attack with Booming Blade Quicken Booming Blade.
Would Draconic Bloodline work as well with plate? Perhaps This:
GOO Warlock 2/Favored Soul Sorc 7
Half Elf
STR: 16
DEX: 10
CON: 14
INT: 8
WIS: 12
CHA: 16
ASI: Either Warcaster or STR bump
Thoughts?
I think that's fine too, but I'm not sure what you meant by draconic with plate (followed by favored soul in the build outline). Regardless of what you pick, if you plan to be mostly melee, I wouldn't overlook AC. The draconic sorcerer's alternate calc doesn't do much in this regard as you can't afford to invest in DEX. And I'm not sure if this is what you are getting at, but the Favored Soul doesn't give armor proficiency (I'm far from an expert, but I think I remember reading that a past iteration did, but they took that away from it). So I still think Stone Sorcery is solid because you will want some CON anyway. With 14 CON and a +1 shield I think you are at 18 AC? Not over the top, but not terrible (plus careful use of the shield spell can help when really needed).
As far as the split, extra attack is optional, but not wasted for a few reasons:
1) Relying on two attacks/round from quicken burns resources. Look at how many sorcery points you will have. For those (possibly not infrequent) times when you need to do your job of hitting bad guys, but can't justify pouring extra resources into it, it will be nice to be able to hit twice.
2) On the other hand, when you really want to show off and burn through resources to take down a baddie fast, you will get three pactsmites per round if you have extra attack (vs two if you rely on only quicken). With 3rd level slots that will be 3x normal attack damage + 1x GFB or BB damage + 18d8, so probably ~110-120 dmg? For rough math I think you can expect about 2/3rds that nova damage if you don't have extra attack. Edit: I'm wrong about this because with 5 lock/4 sorc you would only have 2 3rd level slots so the third attack would use a 2nd level slot (so 3x attack damage + 16d8 pactsmite). The 2 lock/7 sorc would actually be able to spend a 4th and a 3rd level spell (so 2x attack damage + 14d8 pactsmite). Numbers aren't so far apart, but as you level the warlock 5 base should grow an advantage as you are able to spend higher level spell slots on 3x smiting.
3) If you do go with Claw of Acamar, you want extra attack because it has reach and GFB/BB are limited to 5'. If you decide 2 warlock is enough and double casting GFB/BB is going to be your go to, then Mace of Dispater may be better as you'll need to be in 5' range anyway (and the temp HP from fiend pact aren't terrible either...unless you are trying to also pull off some armor of agathys tricks).
4) Keep in mind you might want to do something else with your bonus action anyway (a smite spell if you happen to go with stone sorcery?). In these cases, still having 2 attacks when you take the attack action is nice.
Besides the extra attack, I suggested such an even split because of the ASIs. If you go with a one hander and shield (again, I was assuming stone sorcery) you need war caster, unless I misunderstand how casting and holding items works. Or maybe, since you indicated you don't want to get bogged down in a lot of casting, you can skip this and only cast spells without somantic components during combat and basically reserve all your spell slots for pactsmites. If you do want war caster you are either a human with 2 ASIs with an even split, or a half elf with 1. Without war caster you are a half elf with 2 ASIs (no point in human here). Either way you want STR, CON, and CHA, so having 2 ASIs is nice. A split that only gives 1 (Helf with only 2 warlock levels) is either only getting a single +2 bonus or none at all if he picks up war caster.
You picked pretty balanced stats, but if you really threw caution to the wind on your "dump" stats, you could start Helf with 16/16/16 in your core abilities and have STR and CHA both at 18 when you start the game with the dual ASI split (granted this only gives you 2 points left over, leaving INT at 8 and either DEX or WIS at 8 as well, with the other at 10).
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Ultimately if I were playing this character and seriously wanted to be mostly a consistent melee striker with decent defense, some lockdown, and really good nova potential (without worrying overly much about spellcasting) I would start 5 lock/4 sorc. If I still wanted the nova potential, but was willing to give up some of the consistency in my melee damage for a chance at actually using higher level spells for things outside smiting, I would start 2 warlock/7 sorc.
