Lethargy probably isn't powerful enough imo, given that it's very unlikely for a barbarian to drop out of Frenzy while still in combat. And after combat, lethargy ~doesn't matter.
Disadvantage on Wis STs is kicking the puppy when it's down; barbarians are already bad enough at Wis STs as it is.
I like the -2 AC, especially as it pairs well with Reckless Attack (you're probably already going to be hit anyway, who cares about an additional -2 AC?) and Barbarians' HP+Damage resistance (Barbarians are built around getting hit, so -2 AC is kind of playing to their strengths).
It'd be cool if the AC penalty grew over time, to represent getting more and more lost in your rage and abandoning your defenses. First turn is no penalty, 2nd turn is -1, 3rd turn is -2, etc. As @Stabbey mentions, since it's a video game that'd be super easy to do. Maybe also with the lethargy penalty when you come out of rage...? That might be an interesting cost-benefit analysis..."I'm at a -5 AC, but I'd lose a turn if I ended my rage. Is it worth it?"
