Re: stats, you have at least 4 positive stats before ASIs, and replacing your dex with str in the AC calc doesn't mean you can freely dump dex.

A scaling damage die REALLY doesn't work, and in fact was the original concept. I really don't know what else to say, there's no reason why having a slightly higher damage die for 2 levels is a bad thing, especially when published material already breaks that mold for 4.

Also worth noting is that I've been DMing for a CF barb with d6 attacks alongside a monk for about a year, a d6 strike is the part I'm 100% certain about. Classes don't exist in a vacuum and a d6 gives the same damage as a monk or TWF.

100lbs of muscle doesn't inherently make your punches hurt more. Force is calculated by speed, not strength, especially for punches.

Unarmed strikes are strength based in d&d with martial arts being the exception.

I was juggling using strength vs just giving them a +2 AC (the original idea) but mechanically they end up being more or less the same. Chances are your Strength mod will constantly be around 2 higher than your dex, even at max level.