Does troop research always crush everything else in Dragonfire?

Not always — it depends on your stage. The "research crushes everything" idea comes from end-of-season fights, where a type's research could hit +5,799% (×60). There, yes, it dominates everything.

But in the early game, type research is only a few percent (e.g. Spearmen +5.2%, Archers +4%). At that stage it's comparable to the small ±7% and well below the +20% affinity and the auras (−27.5%).

The relative weight of the layers shifts as you progress:

• Early game (weak research): the dragons (stats/level/stars), the auras and the +20% affinity dominate. Research and ±7% are minor.
• Late game (research in the thousands of percent): research on the type you field crushes everything.

The moral: don't recite a fixed rule. Match your priority to the research you actually have. Early on, tend your auras and affinities; late on, research decides the fight.