The Dominion were scary before the war because we saw them blowing up plenty of ships and people in their very first appearance like the USS Odyssey. Plus the whole "prisoner is really spy" thing.
VOY DID show the Borg attacking and assimilating others, but it still didn't matter to the audience.
Frankly, I find more problems with BoT every time I see it which has lessened my enjoyment of it over the years. That the characterizations and stuff were all taken from a prior movie and pretty much pasted onto existing TOS characters didn't really make me like it much more either.
VOY DID show the Borg attacking and assimilating others, but it still didn't matter to the audience.
Frankly, I find more problems with BoT every time I see it which has lessened my enjoyment of it over the years. That the characterizations and stuff were all taken from a prior movie and pretty much pasted onto existing TOS characters didn't really make me like it much more either.