They are a threat but not to the extent that we saw at Wolf 359, technology has moved on and some of it was inspired by the Borg themselves.
I don't think we will see any ablative armor or transphasic torpedoes as they would make the Borg a joke, which they most definitely are not.
The Borg cube filled with XB's could end up being allies of Picard (he called them victims not monsters), depending on what Seven does in the episode.
The danger is that the Borg could send more Cubes if a connection is re-established but I don't think that is the direction the show is going to take.
There is still the possibility we may get slapped with Control again but that is one possibility among many, Burnham does have the suit so she or Georgiou could go back and warn the Vulcans before the schism, alternatively similarities in the visual imagery could just be coincidence.
That is the problem when you start messing with time, you can pretty much do or undo anything.