Only one new narrative is added (Mustang), so it’s not too hard of an adjustment.

His writing improves with every book. With Iron Gold, he struggles with juggling the four narratives in a way that doesn’t destroy pacing (especially because Lyria’s PoV is so dull).

For what it’s worth, Iron Gold is generally considered the weakest of the series, while Dark Age and Light Bringer have been highly rated (and I would agree with that). So point being, stick with it because the end of Iron Gold and the rest of the series is very very good.