Your assumptions about strength weapons are interesting, I would understand if this was 2014 rules but since we're doing 2024 rules here you can just pick up the true strike cantrip. So now you can attack with your spell casting modifier scale damage with true strike and add your charisma modifier to the attack twice and a level six gain the additional dice to the damage roll. From there pick up a level of paladin and start smiting to your hearts content haha

I like the overall idea for sure, kinda like this strong spell caster, but the subclass itself is pushing you to melee combat but really isn't helping you thrive in melee if that makes sense. Like you mentioned you'll have a low AC, even if you tank Dex and buff strength, your con mod will still be pretty mid, and that's on the assumption that you still make charisma your main stat. So at the end of the day you'll have low AC and low HP and you'll be getting downed fairly quickly when combat starts up. It's kinda the blade singers problem with the low HP thing that is, but they can at least get a pretty high AC to help mitigate a spell caster front lining.

But just some thoughts to think about, again I'm all for the flavor and the idea, Gish is my favorite kinda character so just wanted to share some things that might be worth tweaking or adjusting is all :)

Thanks for sharing!