With Favored Enemy, Rams Might, and no dex requirement for TWF, Tempest Rangers should hit just as hard has a Kensai Power Boosted Fighter with Wep Spec Feats.
That being said, a Fighter will out dps a Tempest due to the speed boosts. A Kensai III will have 11ish speed boosts, that's enough to keep it up when it matters.
1. Tempest III is disproportionately weak. The other two levels give ~4% overall dps, with Tempest III at ~2.5%.
2. Something like making them 110/100 or 105/105 isn't such a bad idea, when you consider a fighter to being like 143/104 on boost, 110/80 off.