Experience in my games is that Double Slice feels a little too good - especially when compared to other fighter feats of the same level. Multiclass rogue feels a little too effective with it.
Maybe make TWF work more like the Double Shot archery feat? That seems a bit more balanced and it does very similar things. Maybe reduce the penalty to -1 on both attacks? -3 on the offhand if it isnt agile?
No, make all the other feats better to match up.
Double Slice is the standard because it actually makes you better, where most of the other feats make you worse when compared to the baseline of just striking with your weapon.
Archery can take a nerf because it doesn't require movement.