Frenzied Strain is antithetical to bounded accuracy.

[Dagungus]

So in 5e bounded accuracy is the defining feature which gives dm's a sense of what the group can handle. The more advanced the group is in their play, the more the dm can raise the CR of creatures.
However, in baldurs gate 3 bounded accuracy is the foundation of the games entire method of advancement, which is combat. having an ability that gives you -1 to hit every time you use a bonus action attack is like purposefully attuning to a cursed item that gives you -5 to hit instead of +3. You are going to end up doing nothing by the end of the fight, and feel completely useless while your casters spam their world ending spells.
I urge you to reconsider balancing this subclass, because knocking 2 creatures prone a fight with enraged throw is not worth the drawbacks. The subclass more or less gets nothing else outside of this either.

[Zygfryd]

So... you end your frenzy to get your attack bonus back up.

It's a great feature if you have surplus attack bonus to spare, eg. from Tavern Brawler or having an enchanted weapon.

Don't forget you also get Reckless Attack.

And the level 6 immunity to charmed and frightened is great.