I'd also argue they're not weaker than the Ninja Storm powers, the Ninja storm rangers are simply better fighters and aren't holding back compared to the Dino Thunder Rangers.
During the fight, the Dino Thunder Rangers match them in strength locks, land plenty of blows and are fighting the Ninja Storm rangers AND a monster AND Kelzacs simultaneously (Kira even states she doesn't want to hurt Tori, indicating the rangers are holding back)
Later, Dr. O does imply they're stronger, saying the Rangers will need "a lot more than what we have to defeat them" but immediately after, reinterates the Dino Thunder rangers are holding back by saying "They are people who are once good, but something happened to them. Until we figure out what, we defend ourselves but we don't destroy them." Right after, in the unmorphed fight, the Dino Thunder Rangers stalemate the Ninja Storm rangers again. After the second fight, Shane even points out the Dino Thunder Rangers "fight like rock stars" implying it's a skill issue.
I'd say they're even, but the Ninja Storm Rangers not holding back because they're evil+superior fighting skills made them the clear winners