You can run
14
10
14
And then run a 17 in your casting stat no issue while keeping the rest 10. If you take an 8 on one you can then take 15 str or con or pump ome into dex if you really want the +2 ac with medium armor.
Halberds give the cleave attack, which certainly can be usefull on fights with lots of mobs like the goblins attack on the grove, and will probably be even better in the harder difficulties where the ai will prioritized swarming squishies.
Abjuation/transmutation/necromancy builds focused on using spell slots for self buffing will naturally like them too, especially the weapons with the brace option so you can reroll damage dice and take the higher
And this isn't even considering the the special magic weapons, so of which are race locked
Pact of the blade doesn't seem to give proficiency
With that build your AC, initiative, and Dex ST will be fairly subpar. Even Half Plate (requiring you to take the Moderately Armored Feat?) with 12 Dex will only give you an AC of 16, which isn't great for a level 4+ character, especially one with low HP. I expect this polearm wielding full caster to constantly be on the verge of death and/or actually unconscious a lot of the time.
Plus, 14 Str still isn't that good. At levels 4+, you'll be going against enemies that are expecting you to have a +6 to-hit, while you'd have a +4. (And if you sacrifice to get 16 Str, you'll have lower AC). And at levels 5+, you won't get Extra Attack and so you'll become ~useless in melee.
Fair point about the blade warlock if true, although I think that's a dumb decision. The whole point is that you become supernaturally proficient with a weapon!!
tl;dr: This mostly seems like a very niche slight benefit for a small subset of builds, and worthless for the remaining ones.
